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Ritanjali SR, Bhandaru N, Mukherjee R. Influence of Initial Film Properties in UVO-Mediated Patterning of an Elastomeric Film Using a TEM Grid. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024. [PMID: 39132929 DOI: 10.1021/acs.langmuir.4c00509] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/13/2024]
Abstract
Ultraviolet irradiation of a cross-linked polydimethylsiloxane (PDMS) Sylgard 184 film in the presence of atmospheric oxygen (UVO) through a bare transmission electron microscope (TEM) sample holding grid is a rather simple and widely utilized technique for creating micropatterned surfaces. The surface oxidation of a Sylgard 184 film due to UVO exposure is associated with densification and the formation of a silica-like surface layer, which under a TEM grid happens only over the exposed areas of the film, resulting in a physicochemical pattern. It is known that the depth (hD) of the features depends on the duration of UVO exposure (tE). In this article, we show for the first time that hD also depends on the initial film thickness (hF) and the cross-linker percentage (CL, ratio of part A to part B) in a Sylgard 184 thin film. We show that for a specific tE, hD progressively decreases with the reduction in hF. On the other hand, hD shows a nonmonotonic dependence with CL, resulting in patterns with maximum depth for CL ≈ 10.0%. We attribute this observation to the combined effect of resistance against the penetration of the propagation front by the rigid substrate as well as stress relaxation within the exposed parts of the film below the propagating front in films with higher CL values leading to the variation of hD. The observation reported here would allow the potential fabrication of polymer films with physicochemical patterns with feature height on demand by a one-step, facile technique.
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Affiliation(s)
- Sushree Ritu Ritanjali
- Instability and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal 721-302, India
| | - Nandini Bhandaru
- Department of Chemical Engineering, Birla Institute of Technology and Science Pilani, Hyderabad Campus, Telangana 500-078, India
| | - Rabibrata Mukherjee
- Instability and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal 721-302, India
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3
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Pandey A, Murmu K, Gooh Pattader PS. Non-equilibrium thermal annealing of a polymer blend in bilayer settings for complex micro/nano-patterning. RSC Adv 2021; 11:10183-10193. [PMID: 35423522 PMCID: PMC8695700 DOI: 10.1039/d1ra00017a] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2021] [Accepted: 02/26/2021] [Indexed: 01/30/2023] Open
Abstract
Micro phase separation in a thin film of a polymer blend leads to interesting patterns on different substrates. A plethora of studies in this field discussed the effect of the surface energy of the underlying tethered polymer brush or substrate on the final morphology of the polymer blend. The conventional process toward the final morphology is rather slow. Here, aiming fast lithography, we induce the kinetically driven morphological evolution by rapid thermal annealing (RTA) of the polymer blend of polystyrene (PS) and polymethylmethacrylate (PMMA) in bilayer settings at a very high temperature. The underlying film consists of untethered constituent homopolymers or their blend or random-co-polymer (RCP). Apart from the phase inversion of the blend on the PS homopolymer, a rich morphology of the blend on the RCP underlayer is uncovered with systematic investigation of the film using sequential washing with selective solvents. The dissolution characteristics and the thermal stability of the constituent polymers corroborated the observation. Based on the understanding of the morphological evolution, fabrication of a complex shaped micro/nano-pattern with multiple length scales is demonstrated using this blend/RCP system. This study shows a novel methodology for easy fabrication of hierarchical small length scale complex structures.
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Affiliation(s)
- Ankur Pandey
- Department of Chemical Engineering, Indian Institute of Technology Guwahati 781039 India
| | - Kaniska Murmu
- Department of Chemical Engineering, Indian Institute of Technology Guwahati 781039 India
| | - Partho Sarathi Gooh Pattader
- Department of Chemical Engineering, Indian Institute of Technology Guwahati 781039 India
- Center for Nanotechnology, Indian Institute of Technology Guwahati 781039 India
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4
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Roy P, Mukherjee R, Bandyopadhyay D, Gooh Pattader PS. Electrodynamic-contact-line-lithography with nematic liquid crystals for template-less E-writing of mesopatterns on soft surfaces. NANOSCALE 2019; 11:16523-16533. [PMID: 31454013 DOI: 10.1039/c9nr05729c] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We report the development of a single-step, template-less and fast pathway, namely, Electrodynamic-Contact-Line-Lithography (ECLL), to write micro to nanopatterns on the surface of a soft polymer film. As a model system, a layer of nematic liquid crystals (NLC), resting on a polymer thin film, was sandwiched between a pair of electrodes emulating the electrowetting on a dielectric (EWOD) setup. Upon the application of electric field, the Maxwell stresses thus generated at the NLC-polymer interface due to the high dielectric contrast stimulated an unprecedented fingering instability at the advancing NLC-polymer-air contact line. In the process, the advancing electrospreading front of NLC left the footprint of an array of micro to nanoscale wells on the polymer surface with a long-range ordering thus unveiling a pathway for maskless patterning of a soft elastic film. Unlike the conventional electric field induced lithography (EFL), the meso-scale morphology was found to follow the short wavelength-scales as the periodicity of the patterns (λc) varied linearly with the thickness of the film (h), (λc∝h). The high dielectric contrast at the NLC-polymer interface and the local fluctuation of the NLC directors ensured a time scale much faster than the same observed for the polymer-air systems.
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Affiliation(s)
- Pritam Roy
- Centre for Nanotechnology, Indian Institute of Technology, Guwahati, Assam 781039, India.
| | - Rabibrata Mukherjee
- Department of Chemical Engineering, Indian Institute of Technology, Kharagpur, West Bengal 721302, India
| | - Dipankar Bandyopadhyay
- Centre for Nanotechnology, Indian Institute of Technology, Guwahati, Assam 781039, India. and Department of Chemical Engineering, Indian Institute of Technology, Guwahati, Assam 781039, India
| | - Partho Sarathi Gooh Pattader
- Centre for Nanotechnology, Indian Institute of Technology, Guwahati, Assam 781039, India. and Department of Chemical Engineering, Indian Institute of Technology, Guwahati, Assam 781039, India
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5
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Sahoo S, Bhandaru N, Mukherjee R. Reversible morphological switching and deformation hysteresis in electric field mediated instability of thin elastic films. SOFT MATTER 2019; 15:3828-3834. [PMID: 30993267 DOI: 10.1039/c8sm02622j] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Reversible morphology switching in a soft elastic film sandwiched between two parallel electrodes when subject to an externally applied electric field is reported herein. In contrast to electric field mediated instability of a thin liquid film, where the instability patterns remain permanent, in the present case the patterns debond completely or partially when the electric field is switched off, depending on whether the gap spacing (dG) between the film and the top electrode is >100 nm or not. The onset of instability is marked with the appearance of isotropic columns when the applied field strength (U) exceeds a critical value (Uc). The subsequent increase in U leads to the gradual transition of the instability patterns from pillars to bi-continuous labyrinths to an array of holes. Complete conformal contact is established between the film and the top electrode at U = UF. When U is reduced, the morphology changes in a reverse sequence. There is a significant level of hysteresis between the bonding and debonding stages, including persistence of the features at much lower voltages due to pinning of the patterns to the top electrode. Complete detachment occurs at a lower voltage UD when dG > 100 nm. The holes fluctuate before complete contact between the film and the top electrode due to competition between the destabilizing electric field and restoring forces due to stretching of the crosslinked polymer matrix.
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Affiliation(s)
- Sumita Sahoo
- Instability and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, West Bengal 721302, India.
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6
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Dhara P, Mukherjee R. Phase transition and dewetting of a 5CB liquid crystal thin film on a topographically patterned substrate. RSC Adv 2019; 9:21685-21694. [PMID: 35518868 PMCID: PMC9066433 DOI: 10.1039/c9ra02552a] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2019] [Accepted: 07/02/2019] [Indexed: 11/21/2022] Open
Abstract
Thermally induced nematic to isotropic (N–I) phase transition and dewetting of 5CB liquid crystal thin films on flat and topographically patterned substrates.
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Affiliation(s)
- Palash Dhara
- Instability and Soft Patterning Laboratory
- Department of Chemical Engineering
- Indian Institute of Technology Kharagpur
- Kharagpur
- India
| | - Rabibrata Mukherjee
- Instability and Soft Patterning Laboratory
- Department of Chemical Engineering
- Indian Institute of Technology Kharagpur
- Kharagpur
- India
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7
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Ghosh UU, Nair S, Das A, Mukherjee R, DasGupta S. Replicating and resolving wetting and adhesion characteristics of a Rose petal. Colloids Surf A Physicochem Eng Asp 2019. [DOI: 10.1016/j.colsurfa.2018.10.028] [Citation(s) in RCA: 50] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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8
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Chakrabarty P, Gogurla N, Bhandaru N, Ray SK, Mukherjee R. Enhanced performance of hybrid self-biased heterojunction photodetector on soft-lithographically patterned organic platform. NANOTECHNOLOGY 2018; 29:505301. [PMID: 30226471 DOI: 10.1088/1361-6528/aae240] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Nanopatterning of the active layer with feature size comparable to the wavelength of visible light is a popular strategy for improving the performance of optoelectronic devices, as these structures enhance the optical path length by light trapping due to combined contribution of multiple scattering, diffraction, and antireflection. Here, we report the fabrication of ZnO/CdS self-biased heterojunction photodetectors on soft lithographically patterned PEDOT:PSS layers with grating geometry. The present study combines the robustness of inorganic devices along with the convenience of easy patterning capability of an organic PEDOT:PSS layer. Patterns with two different line widths (L P = 350 nm, and Lp = 750 nm) have been used in this study to understand the influence of feature dimension on the device performance. We observe enhanced photoluminescence on patterned devices, in comparison to devices fabricated on flat PEDOT:PSS films, which is attributed to the increased interfacial area between the organic and inorganic layers. The spectral response [R( λ )] and specific detectivity [D * ( λ )] are found to be higher for the devices with Lp = 350 nm as compared to other devices due to enhanced absorption within the structures due to confinement of light, which also results in reduced reflectance in devices with Lp = 350 nm.
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Affiliation(s)
- Poulomi Chakrabarty
- School of Nanoscience and Technology, Indian Institute of Technology Kharagpur, West Bengal, 721302, India. Instability and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, West Bengal, 721302, India
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9
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Chen Y, Wang Z, Kulkarni MM, Wang X, Al-Enizi AM, Elzatahry AA, Douglas JF, Dobrynin AV, Karim A. Hierarchically Patterned Elastomeric and Thermoplastic Polymer Films through Nanoimprinting and Ultraviolet Light Exposure. ACS OMEGA 2018; 3:15426-15434. [PMID: 31458199 PMCID: PMC6643988 DOI: 10.1021/acsomega.7b01116] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2018] [Accepted: 10/16/2018] [Indexed: 06/09/2023]
Abstract
The surface relief structure of polymer films over large areas can be controlled by combining nanoscale imprinting and microscale ultraviolet-ozone (UVO) radiation, resulting in hierarchical structured surfaces. First, nanoscale patterns were formed by nanoimprinting elastomer [poly(dimethylsiloxane) (PDMS)] films with a pattern on a digital video disk. Micron-scale patterns were then superimposed on the nanoimprinted PDMS films by exposing them to ultraviolet radiation in oxygen (UVO) through a transmission electron microscopy grid mask having variable microscale patterning. UVO exposure leads to conversion and densification of PDMS to SiO x , leading to micron height relief features that follow a linear scaling relation with pattern dimension. Further, the pattern scopes are shown to collapse into a master curve by normalized feature values. Interestingly, these relief structures preserve the nanoscale features. In this paper, the influence of the self-limiting PDMS densification, wall stress at the boundary of micro-depression, and UVO exposure energy is studied in control of the micro-depression scale. This simple two-step imprinting process involving both nanoimprinting and UV radiation allows for facile fabrication of the dimension adjustable micro-nano hierarchically structures not only on elastomer films but also on thermoplastic polymer films. Coarse-grained molecular dynamics simulations were performed to correlate the surface tension and elastic properties of polymeric materials to the deformation of the pattern structure.
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Affiliation(s)
- Ying Chen
- Department
of Polymer Engineering and Department of Polymer Science, University of Akron, Akron, Ohio 44325, United States
| | - Zilu Wang
- Department
of Polymer Engineering and Department of Polymer Science, University of Akron, Akron, Ohio 44325, United States
| | - Manish M. Kulkarni
- Department
of Polymer Engineering and Department of Polymer Science, University of Akron, Akron, Ohio 44325, United States
- Center for
Nanosciences, Indian Institute of Technology
Kanpur, Kanpur, Uttar Pradesh 208016, India
| | - Xiaoteng Wang
- Department
of Polymer Engineering and Department of Polymer Science, University of Akron, Akron, Ohio 44325, United States
| | - Abdullah M. Al-Enizi
- Chemistry
Department, Faculty of Science, King Saud
University, P.O. Box 2455, Riyadh 11451, Saudi Arabia
| | - Ahmed A. Elzatahry
- Materials
Science and Technology Program, College of Arts and Sciences, Qatar University, P.O. Box 2713, Doha, Qatar
| | - Jack F. Douglas
- Materials
Science and Engineering Division, National
Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Andrey V. Dobrynin
- Department
of Polymer Engineering and Department of Polymer Science, University of Akron, Akron, Ohio 44325, United States
| | - Alamgir Karim
- Department
of Polymer Engineering and Department of Polymer Science, University of Akron, Akron, Ohio 44325, United States
- Department
of Chemical and Biomolecular Engineering, University of Houston, Houston, Texas 77204, United States
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10
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Banik M, Mukherjee R. Fabrication of Ordered 2D Colloidal Crystals on Flat and Patterned Substrates by Spin Coating. ACS OMEGA 2018; 3:13422-13432. [PMID: 31458054 PMCID: PMC6644416 DOI: 10.1021/acsomega.8b02002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2018] [Accepted: 10/05/2018] [Indexed: 06/01/2023]
Abstract
Spin coating is a simple and rapid method for fabricating ordered monolayer colloidal crystals on flat as well as patterned substrates. In this article, we show how a combination of factors, particularly concentration of the dispensed colloidal solution (C n) and spin-coating speed, influences the ordering process. We have performed systematic experiments on different types of substrates with two types of colloidal particles (polystyrene and silica). We also show that even when perfect ordering is achieved at some locations, there might be a significant spatial variation in the deposit morphology over different areas of the sample. Our experiments reveal that higher C n is required for obtaining perfect arrays, as the diameter of the colloids (d D) increases. Interestingly, a combination of higher C n and rotational speed (expressed as revolutions per minute) is required to achieve perfect ordering on a topographically patterned substrate, as compared to that on a flat surface, because of loss of inertia of the particles during outward flow because of impact on the substrate features. Finally, we also identify the relation between the particle diameter and the height of the pattern features to achieve topography-mediated particle ordering.
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Affiliation(s)
- Meneka Banik
- Instability and Soft Patterning Laboratory,
Department of Chemical Engineering, Indian
Institute of Technology Kharagpur, Kharagpur, West Bengal 721302, India
| | - Rabibrata Mukherjee
- Instability and Soft Patterning Laboratory,
Department of Chemical Engineering, Indian
Institute of Technology Kharagpur, Kharagpur, West Bengal 721302, India
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11
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Ghosh A, Bandyopadhyay D, Sharma A. Electric field mediated elastic contact lithography of thin viscoelastic films for miniaturized and multiscale patterns. SOFT MATTER 2018; 14:3963-3977. [PMID: 29736548 DOI: 10.1039/c8sm00428e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Elastic contact lithography (ECL) and electric field lithography (EFL) have both shown significant potential to develop large-area micropatterns on polymeric surfaces. Recently, the major challenges associated with these processes have been the improvement of the aspect ratio and reduction in the size and periodicity of the patterns fabricated. Herein, with the help of non-linear simulations, we show that combining these methods can be one recipe to overcome these limitations. We consider a linear viscoelastic film for the linear and non-linear analyses. In this regard, we explore the role of the moving contactor to improve the aspect ratio of the patterns. The study uncovers that (i) combined destabilizing influences originating from van der Waals and electric field forces ensure smaller timescales and length scales for the instabilities, (ii) the aid from the electric field helps to improve the minimum separation distance so that the contact instability initiates at a larger separation distance, (iii) a long-range ordering can be inflicted on the patterns on the polymer surfaces when electrodes with periodic physicochemical patterns are used and (iv) the strength of the externally applied electric field and the ratio of elastic to viscous compliance of the film play crucial roles in deciding the different modes of debonding of the film - peeling, catastrophic or coalescence. The proposed method can improve the aspect ratio of patterns by ∼9-fold during the peeling mode of debonding. Furthermore, pathways to develop technologically important biomimetic surfaces with multiscale and hierarchical structures have been shown.
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Affiliation(s)
- Abir Ghosh
- Department of Chemical Engineering, Indian Institute of Technology Kanpur, Uttar Pradesh 208016, India.
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12
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Bhandaru N, Karim A, Mukherjee R. Directed ordering of phase separated domains and dewetting of thin polymer blend films on a topographically patterned substrate. SOFT MATTER 2017; 13:4709-4719. [PMID: 28613314 DOI: 10.1039/c7sm00799j] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Substrate pattern guided self-organization of ultrathin and confined polymeric films on a topographically patterned substrate is a useful approach for obtaining ordered meso and nano structures over large areas, particularly if the ordering is achieved during film preparation itself, eliminating any post-processing such as thermal or solvent vapor annealing. By casting a dilute solution of two immiscible polymers, polystyrene (PS) and polymethylmethacrylate (PMMA), from a common solvent (toluene) on a topographically patterned substrate with a grating geometry, we show the formation of self-organized meso patterns with various degrees of ordering. The morphology depends on both the concentration of the dispensed solution (Cn) and the blend composition (RB). Depending on the extent of dewetting during spin coating, the final morphologies can be classified into three distinct categories. At a very low Cn the solution dewets fully, resulting in isolated polymer droplets aligned along substrate grooves (Type 1). Type 2 structures comprising isolated threads with aligned phase separated domains along each substrate groove are observed at intermediate Cn. A continuous film (Type 3) is obtained above a critical concentration (Cn*) that depends on RB. While the extent of ordering of the domains gradually diminishes with an increase in film thickness for Type 3 patterns, the size of the domains remains much smaller than that on a flat substrate, resulting in significant downsizing of the features due to the lateral confinement imposed on the phase separation process by the topographic patterns. Finally, we show that some of these structures exhibit excellent broadband anti-reflection (AR) properties.
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Affiliation(s)
- Nandini Bhandaru
- Instability and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, West Bengal, Pin 721302, India.
| | - Alamgir Karim
- Department of Polymer Engineering and Akron Functional Materials Centre (AFMC), University of Akron, Akron, Ohio 44325, USA
| | - Rabibrata Mukherjee
- Instability and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, West Bengal, Pin 721302, India.
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Bhandaru N, Sharma A, Mukherjee R. Programmable Nanopatterns by Controlled Debonding of Soft Elastic Films. ACS APPLIED MATERIALS & INTERFACES 2017; 9:19409-19416. [PMID: 28610425 DOI: 10.1021/acsami.6b09127] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We report a facile patterning technique capable of creating nanostructures with different feature heights (hS), periodicities (λS), aspect ratios (AR), and duty ratios (DR), using a single grating stamp with fixed feature height hP and periodicity λP. The proposed method relies on controlling the extent of debonding and morphology of the contact instability features, when a rigid patterned stamp is gradually debonded from a soft elastic film to which it was in initial conformal contact. Depending on whether the instability wavelength (λF scales with the film thickness hF as λF ≈ 3hF) and the periodicity of the stamp feature (λP) are commensurate or not, it is possible to obtain features along each stamp protrusion when λF ≈ λP or patterns that span several stripes of the stamp when λF > λP. In both cases, the patterns fabricated during debonding are taller than the original stamp features (hS > hP). We show that hS can be modulated by controlling the extent of debonding as well as the shear modulus of the film (μ). Additionally, when λF > λP, progressive debonding leads to the gradual peeling of replicated features, which, in turn, allows possible tuning of the duty ratio (DR) of the patterns. Finally we show that by the simultaneous modulation of AR, DR, and hS, it becomes possible to create surfaces with controlled wettability.
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Affiliation(s)
- Nandini Bhandaru
- Instability and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur , Kharagpur 721302, West Bengal, India
| | - Ashutosh Sharma
- Department of Chemical Engineering and Nanoscience Center, Indian Institute of Technology Kanpur , Kanpur 208016, Uttar Pradesh, India
| | - Rabibrata Mukherjee
- Instability and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur , Kharagpur 721302, West Bengal, India
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14
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Chaudhari N, Deshpande T, Singh YRG, Patil S, Kulkarni M, Raut J, Sharma A. Cavity shape transformation during peeling on elastic microchannel-patterned substrates filled with a viscous liquid. SOFT MATTER 2017; 13:2394-2401. [PMID: 28282091 DOI: 10.1039/c7sm00016b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Inspired by the detachment mechanics of natural adhesive pads, we studied the change in cavity shape during peel tests on a 10% cross-linked polydimethylsiloxane (PDMS) elastic microchannel filled with 1% cross-linked viscous PDMS liquid (patterned bilayer). During peeling, we explored cavity shape as a function of microchannel dimensions and correlated the dimensionless cavity shape factor (CSF) and characteristic stress decay length, K-1. The peel test on the liquid-filled elastic microchannel shows three distinct cavity-shape regimes, elliptical, circular, and binary, based on the values of CSF and K-1. Such cavity formation and shape regimes could be important for improving the design of pressure-sensitive adhesives.
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Affiliation(s)
- Nayantika Chaudhari
- Department of Chemical Engineering and Center for Nanosciences, Indian Institute of Technology, Kanpur-208016, UP, India.
| | - Tushar Deshpande
- Department of Chemical Engineering and Center for Nanosciences, Indian Institute of Technology, Kanpur-208016, UP, India.
| | - Yogesh R G Singh
- Department of Chemical Engineering and Center for Nanosciences, Indian Institute of Technology, Kanpur-208016, UP, India.
| | - Sandip Patil
- Department of Chemical Engineering and Center for Nanosciences, Indian Institute of Technology, Kanpur-208016, UP, India.
| | - Manish Kulkarni
- Department of Chemical Engineering and Center for Nanosciences, Indian Institute of Technology, Kanpur-208016, UP, India.
| | - Janhavi Raut
- Unilever R&D, 64 Main Road, Whitefield, Bangalore 560066, India
| | - Ashutosh Sharma
- Department of Chemical Engineering and Center for Nanosciences, Indian Institute of Technology, Kanpur-208016, UP, India.
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15
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LI FENG, WANG PENGFEI, YANG SHUNLI, ZHAO GUIPING. CONTACT INSTABILITY OF NON-PLANAR ELASTOMERIC SURFACES. J MECH MED BIOL 2016. [DOI: 10.1142/s0219519416500974] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Contact surfaces between non-planar elastomers widely present in the industrial and biomedical fields, such as corrugated mats and biological fillers. Probing out the mechanical instability of these contact surfaces could greatly contribute to the efficiency, safety and durability of the related structures. In this paper, we numerically studied the contact instability of non-planar elastomeric surfaces with typical projections (i.e., circular and triangle projections) by proposing an instability criterion and using the finite element method. Moreover, we studied the effects of several key factors (e.g., the geometrical parameters and the friction coefficients of the surfaces) on the critical force of the mechanical instability. It is found that with comparable geometric sizes, the surface with circular projections is more effective to enhance the contact stability than that with triangle projections. A larger slope and curvature radius result in weaker stability while a larger friction coefficient plays a positive role for the stability. However, with increasing friction coefficient, the maximum force presents smaller and smaller changes and further improvement of contact stability mainly depends on the changes of the number of projections. These investigations may improve the understanding of the mechanical instability of non-planar elastomeric surfaces and contribute to achieve better designs of related structures.
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Affiliation(s)
- FENG LI
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, Beijing 100094, P. R. China
- Key Laboratory of Road Structure & Material, Research Institute of Highway, Ministry of Transport, Beijing 100088, P. R. China
| | - PENGFEI WANG
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, Beijing 100094, P. R. China
- Bioinspired Engineering and Biomechanics Center (BEBC), Xi'an Jiaotong University, Xi'an 710049, P. R. China
| | - SHUNLI YANG
- Bioinspired Engineering and Biomechanics Center (BEBC), Xi'an Jiaotong University, Xi'an 710049, P. R. China
| | - GUIPING ZHAO
- Bioinspired Engineering and Biomechanics Center (BEBC), Xi'an Jiaotong University, Xi'an 710049, P. R. China
- School of Aerospace, Xi'an Jiaotong University, Xi'an 710049, P. R. China
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16
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Bhandaru N, Das A, Mukherjee R. Confinement induced ordering in dewetting of ultra-thin polymer bilayers on nanopatterned substrates. NANOSCALE 2016; 8:1073-1087. [PMID: 26658720 DOI: 10.1039/c5nr06690e] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We report the dewetting of a thin bilayer of polystyrene (PS) and poly(methylmethacrylate) (PMMA) on a topographically patterned nonwettable substrate comprising an array of pillars, arranged in a square lattice. With a gradual increase in the concentration of the PMMA solution (Cn-PMMA), the morphology of the bottom layer changes to: (1) an aligned array of spin dewetted droplets arranged along substrate grooves at very low Cn-PMMA; (2) an interconnected network of threads surrounding each pillar at intermediate Cn-PMMA; and (3) a continuous bottom layer at higher Cn-PMMA. On the other hand the morphology of the PS top layer depends largely on the nature of the pre-existing bottom layer, in addition to Cn-PS. An ordered array of PMMA core-PS shell droplets forms right after spin coating when both Cn-PMMA and Cn-PS are very low. Bilayers with all other initial configurations evolve during thermal annealing, resulting in a variety of ordered structures. Unique morphologies realized include laterally coexisting structures of the two polymers confined within the substrate grooves due to initial rupture of the bottom layer on the substrate followed by a squeezing flow of the top layer; an array of core-shell and single polymer droplets arranged in an alternating order etc., to highlight a few. Such structures cannot be fabricated by any stand-alone lithography technique. On the other hand, in some cases the partially dewetted bottom layer imparts stability to an intact top PS layer against dewetting. Apart from ordering, under certain specific conditions significant miniaturization and downsizing of dewetted feature periodicity and dimension as compared to dewetting of a single layer on a flat substrate is observed. With the help of a morphology phase diagram we show that ordering is achieved over a wide combination of Cn-PMMA and Cn-PS, though the morphology and dewetting pathway differs significantly with variation in the thickness of the individual layers.
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Affiliation(s)
- Nandini Bhandaru
- Instability and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, West Bengal, Pin 721302, India.
| | - Anuja Das
- Instability and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, West Bengal, Pin 721302, India.
| | - Rabibrata Mukherjee
- Instability and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, West Bengal, Pin 721302, India.
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17
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Mukherjee R, Sharma A. Instability, self-organization and pattern formation in thin soft films. SOFT MATTER 2015; 11:8717-8740. [PMID: 26412507 DOI: 10.1039/c5sm01724f] [Citation(s) in RCA: 73] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The free surface of a thin soft polymer film is often found to become unstable and self-organizes into various meso-scale structures. In this article we classify the instability of a thin polymer film into three broad categories, which are: category 1: instability of an ultra-thin (<100 nm) viscous film engendered by amplification of thermally excited surface capillary waves due to interfacial dispersive van der Waals forces; category 2: instability arising from the attractive inter-surface interactions between the free surface of a soft film exhibiting room temperature elasticity and another rigid surface in its contact proximity; and category 3: instability caused by an externally applied field such as an electric field or a thermal gradient, observed in both viscous and elastic films. We review the salient features of each instability class and highlight how characteristic length scales, feature morphologies, evolution pathways, etc. depend on initial properties such as film thickness, visco-elasticity (rheology), residual stress, and film preparation conditions. We emphasize various possible strategies for aligning and ordering of the otherwise isotropic structures by combining the essential concepts of bottom-up and top-down approaches. A perspective, including a possible future direction of research, novelty and limitations of the methods, particularly in comparison to the existing patterning techniques, is also presented for each setting.
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Affiliation(s)
- Rabibrata Mukherjee
- Instability and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology, Kharagpur, 721 302, India.
| | - Ashutosh Sharma
- Department of Chemical Engineering and Nano-science Center, Indian Institute of Technology, Kanpur, 208016, India.
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18
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Roy S, Bandyopadhyay D, Karim A, Mukherjee R. Interplay of Substrate Surface Energy and Nanoparticle Concentration in Suppressing Polymer Thin Film Dewetting. Macromolecules 2015. [DOI: 10.1021/ma501262x] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Sudeshna Roy
- Instability
and Soft Patterning Laboratory, Department of Chemical Engineering, IIT Kharagpur, Kharagpur, West Bengal 721302, India
| | | | | | - Rabibrata Mukherjee
- Instability
and Soft Patterning Laboratory, Department of Chemical Engineering, IIT Kharagpur, Kharagpur, West Bengal 721302, India
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19
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Bhandaru N, Das A, Salunke N, Mukherjee R. Ordered alternating binary polymer nanodroplet array by sequential spin dewetting. NANO LETTERS 2014; 14:7009-16. [PMID: 25420041 DOI: 10.1021/nl5033205] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
We report a facile technique for fabricating an ordered array of nearly equal-sized mesoscale polymer droplets of two constituent polymers (polystyrene, PS and poly(methyl methacrylate), PMMA) arranged in an alternating manner on a topographically patterned substrate. The self-organized array of binary polymers is realized by sequential spin dewetting. First, a dilute solution of PMMA is spin-dewetted on a patterned substrate, resulting in an array of isolated PMMA droplets arranged along the substrate grooves due to self-organization during spin coating itself. The sample is then silanized with octadecyltrichlorosilane (OTS), and subsequently, a dilute solution of PS is spin-coated on to it, which also undergoes spin dewetting. The spin-dewetted PS drops having a size nearly equal to the pre-existing PMMA droplets position themselves between two adjacent PMMA drops under appropriate conditions, forming an alternating binary polymer droplet array. The alternating array formation takes place for a narrow range of solution concentration for both the polymers and depends on the geometry of the substrate. The size of the droplets depends on the extent of confinement, and droplets as small as 100 nm can be obtained by this method, on a suitable template. The findings open up the possibility of creating novel surfaces having ordered multimaterial domains with a potential multifunctional capability.
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Affiliation(s)
- Nandini Bhandaru
- Instability and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur , Kharagpur, West Bengal 721302, India
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20
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Annepu H, Sarkar J. Miniaturized pattern formation in elastic films cast on sinusoidally patterned substrates. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:12278-12286. [PMID: 25238212 DOI: 10.1021/la502933c] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The various morphologies that are formed when van der Waals forces or electric field is induced between film cast on a sinusoidal substrate and in contact proximity with a contactor or electrode are studied. Remarkably smaller length scales are achieved (λc < 2.96h) than those obtained with films cast on flat substrates. With van der Waals interactions, the patterns are uniformly formed throughout the film but are not regularly ordered. When electric field is used at critical voltage, more ordered, localized patterns are formed at the zones of large local interaction strengths. When these patterns are evolved by increasing the applied voltage, coexistence of all three phases-cavities, stripes, and columns-is observed throughout the film. The localized patterns that are initially formed vary with the voltage applied and strongly dictate the phases of evolution. A patterned substrate/patterned contactor assembly can be made to operate like its unpatterned counterpart by making the interaction strength same everywhere and yet yield uniform, regularly ordered, highly miniaturized patterns. Such patterns are very useful in various applications like microfluidics; they are formed with great ease and can be morphologically tuned by tuning the externally applied electric field.
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Affiliation(s)
- Hemalatha Annepu
- Chemical Engineering Department, Indian Institute of Technology Delhi , New Delhi 110 016, India
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21
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Dey R, Raj M K, Bhandaru N, Mukherjee R, Chakraborty S. Tunable hydrodynamic characteristics in microchannels with biomimetic superhydrophobic (lotus leaf replica) walls. SOFT MATTER 2014; 10:3451-3462. [PMID: 24647804 DOI: 10.1039/c4sm00037d] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The present work comprehensively addresses the hydrodynamic characteristics through microchannels with lotus leaf replica (exhibiting low adhesion and superhydrophobic properties) walls. The lotus leaf replica is fabricated following an efficient, two-step, soft-molding process and is then integrated with rectangular microchannels. The inherent biomimetic, superhydrophobic surface-liquid interfacial hydrodynamics, and the consequential bulk flow characteristics, are critically analyzed by the micro-particle image velocimetry technique. It is observed that the lotus leaf replica mediated microscale hydrodynamics comprise of two distinct flow regimes even within the low Reynolds number paradigm, unlike the commonly perceived solely apparent slip-stick dominated flows over superhydrophobic surfaces. While the first flow regime is characterized by an apparent slip-stick flow culminating in an enhanced bulk throughput rate, the second flow regime exhibits a complete breakdown of the aforementioned laminar and uni-axial flow model, leading to a predominantly no-slip flow. Interestingly, the critical flow condition dictating the transition between the two hydrodynamic regimes is intrinsically dependent on the micro-confinement effect. In this regard, an energetically consistent theoretical model is also proposed to predict the alterations in the critical flow condition with varying microchannel configurations, by addressing the underlying biomimetic surface-liquid interfacial conditions. Hence, the present research endeavour provides a new design-guiding paradigm for developing multi-functional microfluidic devices involving biomimetic, superhydrophobic surfaces, by judicious exploitation of the tunable hydrodynamic characteristics in the two regimes.
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Affiliation(s)
- Ranabir Dey
- Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721 302, West Bengal, India.
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Roy S, Bhandaru N, Das R, Harikrishnan G, Mukherjee R. Thermally tailored gradient topography surface on elastomeric thin films. ACS APPLIED MATERIALS & INTERFACES 2014; 6:6579-88. [PMID: 24697617 DOI: 10.1021/am500163s] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
We report a simple method for creating a nanopatterned surface with continuous variation in feature height on an elastomeric thin film. The technique is based on imprinting the surface of a film of thermo-curable elastomer (Sylgard 184), which has continuous variation in cross-linking density introduced by means of differential heating. This results in variation of viscoelasticity across the length of the surface and the film exhibits differential partial relaxation after imprinting with a flexible stamp and subjecting it to an externally applied stress for a transient duration. An intrinsic perfect negative replica of the stamp pattern is initially created over the entire film surface as long as the external force remains active. After the external force is withdrawn, there is partial relaxation of the applied stresses, which is manifested as reduction in amplitude of the imprinted features. Due to the spatial viscoelasticity gradient, the extent of stress relaxation induced feature height reduction varies across the length of the film (L), resulting in a surface with a gradient topography with progressively varying feature heights (hF). The steepness of the gradient can be controlled by varying the temperature gradient as well as the duration of precuring of the film prior to imprinting. The method has also been utilized for fabricating wettability gradient surfaces using a high aspect ratio biomimetic stamp. The use of a flexible stamp allows the technique to be extended for creating a gradient topography on nonplanar surfaces as well. We also show that the gradient surfaces with regular structures can be used in combinatorial studies related to pattern directed dewetting.
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Affiliation(s)
- Sudeshna Roy
- Instability and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur 721302, India
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23
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Bhandaru N, Roy S, Suruchi, Harikrishnan G, Mukherjee R. Lithographic Tuning of Polymeric Thin Film Surfaces by Stress Relaxation. ACS Macro Lett 2013; 2:195-200. [PMID: 35581881 DOI: 10.1021/mz300577d] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We report a facile soft lithography (SL) technique that allows fabrication of patterned polymeric surfaces with feature height varying between 0 and h0, using a single stamp. The method relies on the partial relaxation of the applied stress in a viscoelastic polymer thin film imprinted under a transient external load using a flexible stamp. The applicability of the technique is demonstrated for thermosetting (rubbery) as well as thermoplastic (glassy) polymers over a wide range of lateral dimensions. The lateral dimension and the periodicity of imprinted patterns remain identical to that of the original stamp. The method has potential applications in creating templates for performing combinatorial experiments related to wetting and dewetting studies, adhesion, nanotribology, microfluidics, etc.
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Affiliation(s)
- Nandini Bhandaru
- Instability
and Soft Petterning Laboratory, Department
of Chemical Engineering, Indian Institute of Technology Kharagpur, West Bengal, 721 302, India
| | - Sudeshna Roy
- Instability
and Soft Petterning Laboratory, Department
of Chemical Engineering, Indian Institute of Technology Kharagpur, West Bengal, 721 302, India
| | - Suruchi
- Instability
and Soft Petterning Laboratory, Department
of Chemical Engineering, Indian Institute of Technology Kharagpur, West Bengal, 721 302, India
| | - G. Harikrishnan
- Instability
and Soft Petterning Laboratory, Department
of Chemical Engineering, Indian Institute of Technology Kharagpur, West Bengal, 721 302, India
| | - Rabibrata Mukherjee
- Instability
and Soft Petterning Laboratory, Department
of Chemical Engineering, Indian Institute of Technology Kharagpur, West Bengal, 721 302, India
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Roy S, Biswas D, Salunke N, Das A, Vutukuri P, Singh R, Mukherjee R. Control of Morphology in Pattern Directed Dewetting of a Thin Polymer Bilayer. Macromolecules 2013. [DOI: 10.1021/ma3018525] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Sudeshna Roy
- Department of Chemical
Engineering, Indian Institute of Technology, Kharagpur, West Bengal, 721
302, India
| | - Debarati Biswas
- Department of Chemical
Engineering, Indian Institute of Technology, Kharagpur, West Bengal, 721
302, India
| | - Namrata Salunke
- Department of Chemical
Engineering, Indian Institute of Technology, Kharagpur, West Bengal, 721
302, India
| | - Ajit Das
- Department of Chemical
Engineering, Indian Institute of Technology, Kharagpur, West Bengal, 721
302, India
| | - Pavanaphani Vutukuri
- Department of Chemical
Engineering, Indian Institute of Technology, Kharagpur, West Bengal, 721
302, India
| | - Ravdeep Singh
- Department of Chemical
Engineering, Indian Institute of Technology, Kharagpur, West Bengal, 721
302, India
| | - Rabibrata Mukherjee
- Department of Chemical
Engineering, Indian Institute of Technology, Kharagpur, West Bengal, 721
302, India
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25
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Annepu H, Sarkar J. Squeezing instabilities and delamination in elastic bilayers: a linear stability analysis. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2012; 86:051604. [PMID: 23214790 DOI: 10.1103/physreve.86.051604] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2012] [Indexed: 06/01/2023]
Abstract
A linear stability analysis is presented to understand the instabilities that arise in an elastic bilayer, consisting of a very thin bottom layer (thickness < 100 nm) that acts as a wetting film and a top layer that acts as an adhesive film, when placed in contact proximity with an external rigid contactor. Depending on whichever layer is more compliant, "squeezing modes" of instability with a variety of length scales ranging from <<3h to <<3h (h: bilayer thickness) are found to be possible. The least length scales obtained are 0.1h. The squeezing instabilities are, however, accompanied by delamination of the film-film interface. The instability length scales, the strength of interactions required, and the delamination decrease as the compliance of the top film increases. Surface tension effects are found to have a stabilizing influence which increases the instability length scales and decreases the degree of delamination at the cost of high interaction penalty.
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Affiliation(s)
- Hemalatha Annepu
- Department of Chemical Engineering, Indian Institute of Technology Delhi, New Delhi 110 016, India
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26
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Roy S, Mukherjee R. Ordered to isotropic morphology transition in pattern-directed dewetting of polymer thin films on substrates with different feature heights. ACS APPLIED MATERIALS & INTERFACES 2012; 4:5375-85. [PMID: 22999159 DOI: 10.1021/am301311d] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Controlled dewetting of a thin polymer film on a topographically patterned substrate is an interesting approach for aligning isotropic dewetted structures. In this article, we investigate the influence of substrate feature height (H(S)) on the dewetting pathway and final pattern morphology by studying the dewetting of polystyrene (PS) thin films on grating substrates with identical periodicity (λ(P) = 1.5 μm), but H(S) varying between 10 nm and 120 nm. We identify four distinct categories of final dewetted morphology, with different extent of ordering: (1) array of aligned droplets (H(S) ≈ 120 nm); (2) aligned undulating ribbons (H(S) ≈ 70-100 nm); (3) multilength scale structures with coexisting large droplets uncorrelated to the substrate and smaller droplets/ribbons aligned along the stripes (H(S) ≈ 40-60 nm); and (4) large droplets completely uncorrelated to the substrate (H(S) < 25 nm). The distinct morphologies across the categories are attributed to two major factors: (a) whether the as-cast film is continuous (H(S)≤ 80 nm) or discontinuous (H(S)≥ 100 nm) and (b) in case of a continuous film, whether the film ruptures along each substrate stripe (H(S)≥ 70 nm) or with nucleation of random holes that are not correlated to the substrate features (H(S)≤ 60 nm). While the ranges of H(S) values indicated in the parentheses are valid for PS films with an equivalent thickness (h(E)) ≈ 50.3 nm on a flat substrate, a change in h(E) merely alters the cut-off values of H(S), as the final dewetted morphologies and transition across categories remain generically unaltered. We finally show that the structures obtained by dewetting on different H(S) substrates exhibits different levels of hydrophobicity because of combined spatial variation of chemical and topographic contrast along the surface. Thus, the work reported in this article can find potential application in fabricating surfaces with controlled wettability.
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Affiliation(s)
- Sudeshna Roy
- Department of Chemical Engineering, Indian Institute of Technology-Kharagpur, West Bengal, 721 302, India
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27
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Deb Roy R, Sil D, Jana S, Bhandaru N, Bhadra SK, Biswas PK, Mukherjee R. Creation of Self-Organized Complex Meso Patterns in Sol–Gel Thin Films by Confined Capillary Dynamics. Ind Eng Chem Res 2012. [DOI: 10.1021/ie300012m] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
| | | | | | - Nandini Bhandaru
- Department of Chemical Engineering, Indian Institute of Technology Kharagpur, West Bengal 721 302, India
| | | | | | - Rabibrata Mukherjee
- Department of Chemical Engineering, Indian Institute of Technology Kharagpur, West Bengal 721 302, India
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28
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Roy S, Ansari KJ, Jampa SSK, Vutukuri P, Mukherjee R. Influence of substrate wettability on the morphology of thin polymer films spin-coated on topographically patterned substrates. ACS APPLIED MATERIALS & INTERFACES 2012; 4:1887-1896. [PMID: 22468781 DOI: 10.1021/am300201a] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We show that the morphology of a thin polymer film spin coated directly on to a topographically patterned substrate is strongly influenced by the wettability of the substrate, in addition to other well-known parameters such as concentration of the polymer solution (c(n)), spin speed (RPM), and spin duration. Similar to spin coating on a flat surface, (1, 2) on a topographically patterned substrate as well, a continuous film forms only above a critical polymer solution concentration (c(t)*), for a specific RPM and dispensed drop volume. It is believed that for c(n) > c(t)*, the resulting continuous film on a topographically patterned substrate has an undulating top surface, where the surface undulations are in phase with the underlying substrate patterns. (3) On the basis of experiments involving spin coating of polymer thin films on topographically patterned grating substrates, we show that the surface undulations on the film are in phase with the substrate patterns only when the substrate is completely wetted (CW) by the solvent. In contrast, when the substrate is partially wetted (PW) by the solvent, then the undulations are 180° out of phase with respect to the substrate patterns. We further show that for c(n) < c(t)*, a variety of ordered and disordered structures, like array of aligned droplets, isolated strips of polymers, etc., result on both CW and PW substrates, depending on c(n).
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Affiliation(s)
- Sudeshna Roy
- Department of Chemical Engineering, Indian Institute of Technology Kharagpur, West Bengal, India
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