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Das T, Lookman T, Bandi MM. A minimal description of morphological hierarchy in two-dimensional aggregates. SOFT MATTER 2015; 11:6740-6746. [PMID: 26107688 DOI: 10.1039/c5sm01222h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
A dimensionless parameter Λ is proposed to describe a hierarchy of morphologies in two-dimensional (2D) aggregates formed due to varying competition between short-range attraction and long-range repulsion. Structural transitions from finite non-compact to compact to percolated structures are observed in the configurations simulated by molecular dynamics at a constant temperature and density. Configurational randomness across the transition, measured by the two-body excess entropy S2, exhibits data collapse with the average potential energy [small epsilon, Greek, macron] of the systems. Independent master curves are presented among S2, the reduced second virial coefficient B2* and Λ, justifying this minimal description. This work lays out a coherent basis for the study of 2D aggregate morphologies relevant to diverse nano- and bio-processes.
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Affiliation(s)
- Tamoghna Das
- Collective Interactions Unit, OIST Graduate University, Onna, Okinawa 9040495, Japan.
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Chandran S, Dold S, Buvignier A, Krannig KS, Schlaad H, Reiter G, Reiter R. Tuning Morphologies of Langmuir Polymer Films Through Controlled Relaxations of Non-Equilibrium States. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:6426-6435. [PMID: 26000718 DOI: 10.1021/acs.langmuir.5b01212] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Langmuir polymers films (LPFs) frequently form nonequilibrium states which are manifested in a decay of the surface pressure with time when the system is allowed to relax. Monitoring and manipulating the temporal evolution of these relaxations experimentally helps to shed light on the associated molecular reorganization processes. We present a systematic study based on different compression protocols and show how these reorganization processes impact the morphology of LPFs of poly(γ-benzyl-L-glutamate)(PBLG), visualized by means of atomic force microscopy. Upon continuous compression, a fibrillar morphology was formed with a surface decorated by squeezed-out islands. By contrast, stepwise compression promoted the formation of a fibrillar network with a bimodal distribution of fibril diameters, caused by merging of fibrils. Finally, isobaric compression induced in-plane compaction of the monolayer. We correlate these morphological observations with the kinetics of the corresponding relaxations, described best by a sum of two exponential functions with different time scales representing two molecular processes. We discuss the observed kinetics and the resulting morphologies in the context of nucleation and growth, characteristic for first-order phase transitions. Our results demonstrate that the preparation conditions of LPFs have tremendous impact on ordering of the molecules and hence various macroscopic properties of such films.
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Affiliation(s)
| | - Stefanie Dold
- †Institute of Physics, Albert Ludwigs Universität Freiburg, Freiburg 79085, Germany
| | - Amaury Buvignier
- ‡Ecole Nationale Superieure de Chimie de Rennes, 35708 Rennes Cedex 7, France
| | - Kai-Steffen Krannig
- §Department of Colloid Chemistry, Max Planck Institute of Colloids and Interfaces, Potsdam D-14424, Germany
| | - Helmut Schlaad
- §Department of Colloid Chemistry, Max Planck Institute of Colloids and Interfaces, Potsdam D-14424, Germany
- ∥Institute of Chemistry, Universität Potsdam, Potsdam D-14476, Germany
| | - Günter Reiter
- †Institute of Physics, Albert Ludwigs Universität Freiburg, Freiburg 79085, Germany
- #Freiburg Centre for Interactive Materials and Bio-inspired Technologies, Albert Ludwigs Universität Freiburg, Freiburg 79085, Germany
- ¶Freiburg Materials Research Center, Albert Ludwigs Universität Freiburg, Freiburg 79085, Germany
| | - Renate Reiter
- †Institute of Physics, Albert Ludwigs Universität Freiburg, Freiburg 79085, Germany
- ¶Freiburg Materials Research Center, Albert Ludwigs Universität Freiburg, Freiburg 79085, Germany
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53
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Thapar V, Hanrath T, Escobedo FA. Entropic self-assembly of freely rotating polyhedral particles confined to a flat interface. SOFT MATTER 2015; 11:1481-1491. [PMID: 25601423 DOI: 10.1039/c4sm02641a] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The self-assembly of hard polyhedral particles confined to a flat interface is studied using Monte Carlo simulations. The particles are pinned to the interface by restricting their movement in the direction perpendicular to it while allowing their free rotations. The six different polyhedral shapes studied in this work are selected from a family of truncated cubes defined by a truncation parameter, s, which varies from cubes (s = 0) via cuboctahedra (s = 0.5) to octahedra (s = 1). Our results suggest that shapes with small values of s show square-like behavior whereas shapes with large values of s tend to show more disc-like behavior. At an intermediate value of s = 0.4, the phase behavior of the system shows both square-like and disc-like features. The results are also compared with the phase behavior of 3D bulk polyhedra and of 2D rounded hard squares. Both comparisons reveal key similarities in the number and sequence of mesophases and solid phases observed. These insights on 2D entropic self-assembly of polyhedral particles is a first step toward understanding the self-assembly of particles at fluid-fluid interfaces, which is driven by a complex interplay of entropic and enthalpic forces. A first-order analysis of the particle-surface energies associated with a fluid-fluid interface indicates that such enthalpic interactions will be particularly important in determining particle orientation behavior at low to intermediate concentrations.
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Affiliation(s)
- V Thapar
- School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, USA.
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54
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Zhang L, Jiang L, Liu Y, Yin Q. Ionic strength-modulated catalytic efficiency of a multienzyme cascade nanoconfined on charged hierarchical scaffolds. RSC Adv 2015. [DOI: 10.1039/c5ra04512f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Understanding the effect of ionic strength on the efficiency of this enzyme cascade within charged hierarchical nanospace is not only fundamentally interesting, but also important for translating biochemical pathways to noncellular environments.
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Affiliation(s)
- Ling Zhang
- DSAPM Lab
- PCFM Lab
- GDHPPC Lab and OFCM Institute
- School of Chemistry and Chemical Engineering
- Sun Yat-Sen University
| | - Li Jiang
- DSAPM Lab
- PCFM Lab
- GDHPPC Lab and OFCM Institute
- School of Chemistry and Chemical Engineering
- Sun Yat-Sen University
| | - Yuan Liu
- DSAPM Lab
- PCFM Lab
- GDHPPC Lab and OFCM Institute
- School of Chemistry and Chemical Engineering
- Sun Yat-Sen University
| | - Qihe Yin
- DSAPM Lab
- PCFM Lab
- GDHPPC Lab and OFCM Institute
- School of Chemistry and Chemical Engineering
- Sun Yat-Sen University
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55
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Liu Y, Liu Y, Tao P, Shang W, Song C, Deng T. Vertical segregation in the self-assembly of nanoparticles at the liquid/air interface. NANOSCALE 2014; 6:14662-14666. [PMID: 25374387 DOI: 10.1039/c4nr04779f] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Vertical segregation was induced by the size-dependent charge neutralization during the one-step interfacial self-assembly of colloidal gold nanoparticles with bimodal size distribution. This self-assembly approach also can assemble particles with tunable compositions into layered films.
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Affiliation(s)
- Yanming Liu
- State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China.
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56
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Salerno KM, Bolintineanu DS, Lane JMD, Grest GS. High strength, molecularly thin nanoparticle membranes. PHYSICAL REVIEW LETTERS 2014; 113:258301. [PMID: 25554912 DOI: 10.1103/physrevlett.113.258301] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2014] [Indexed: 05/19/2023]
Abstract
The unique strength observed in molecular thin films consisting of assemblies of nanoparticles encoded with short organic chains opens an intriguing new realm of controllable materials. Here the fundamental mechanisms underlying this unique mechanical strength are probed by molecular dynamics simulations. Using nanoparticles encoded with short hydrocarbon chains, we show that the mechanical response and failure of single nanoparticle thick membranes depend on subtle changes of the coating. Extremely high moduli were observed in agreement with experiment. We calculate Young's modulus for the membrane system based on properties of the individual components and find that ligand end-group interactions explain the observed changes in mechanical properties. Specifically, for dodecanethiol chains on 6 nm diameter gold cores, Young's modulus is 2.5 GPa for CH_{3} terminated chains and increases by 50% when end groups are replaced by COOH.
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Affiliation(s)
| | | | - J Matthew D Lane
- Sandia National Laboratories, Albuquerque, New Mexico, 87185, USA
| | - Gary S Grest
- Sandia National Laboratories, Albuquerque, New Mexico, 87185, USA
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