Hydrogen-bond structure at the interfaces between water/poly(methyl methacrylate), water/poly(methacrylic acid), and water/poly(2-aminoethylmethacrylamide)

Peculiar Behavior of Methyl Methacrylate Emulsion Polymerization-Induced Self-Assembly Mediated by RAFT Using Poly(Methacrylic Acid) Macromolecular Chain Transfer Agent

Reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization of methyl methacrylate (MMA) is successfully performed in water in the presence of a poly(methacrylic acid) (PMAA) macromolecular chain transfer agent (macroCTA) leading to the formation of self-stabilized PMAA-b-PMMA amphiphilic block copolymer particles. At pH 3.7, the reactions are well-controlled with narrow molar mass distributions. Increasing the initial pH, particularly above 5.6, results in a partial loss of reactivity of the PMAA macroCTA. The effect of the degree of polymerization (DPn) of the PMMA block, the solids content, the nature of the hydrophobic segment, and the pH on the morphology of the obtained diblock copolymer particles is then investigated. Worm-like micelles are formed for a DPn of PMMA of 20 (PMMA20), while "onion-like" particles and spherical vesicles are obtained for PMMA30 and PMMA50, respectively. In contrast, spherical particles are obtained for the DPns higher than 150. This unusual evolution of particle morphologies upon increasing the DPn of the PMMA block seems to be related to hydrogen bonds between hydrophilic MAA and hydrophobic MMA units.

Light-Operated Transient Unilateral Adhesive Hydrogel for Comprehensive Prevention of Postoperative Adhesions

Dislocation of anti-adhesion materials, non-specific tissue adhesion, and the induction of secondary fibrinolysis disorders are the main challenges faced by postoperative anti-adhesion materials. Herein, a self-leveling transient unilateral adhesive hydrogel is custom-designed to conquer these challenges with a theoretically calculated and dual-step tailored gellan gum (GG) as the sole agent. First, the maximum gelation temperature of GG is lowered from 42-25 °C through controlled perturbation of intra- and inter-molecular hydrogen bonds, which is achieved by employing the methacrylic anhydride as a "hydrogen bond's perturbator" to form methacrylate GG (MeGG). Second, the "self-leveling" injectability and wound shape adaptably are endowed by the formation of borate-diol complexed MeGG (BMeGG). Finally, the transient unilateral tissue-adhesive hydrogel (BMeGG-H) barrier is prepared through photo-controlled cross-linking of reactive alkenyl groups. This degradable hydrogel demonstrates favorable rheological properties, light-controlled unilateral adhesion properties, biocompatibility, anti-fibrin adhesion, and anti-cell adhesion properties in vitro. Comprehensive regulation of the fibrinolysis balance toward non-adhesion is conformed in a rat model after intra-abdominal surgery via anti-autoinflammatory response, intestinal wall integrity repair, and Tissue plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1) balance adjustment. Notably, the 14th day anti-adhesion effective rate is 100%, indicating its significant potential in clinical applications for postoperative anti-adhesion.

Increasing contrast in water-embedded particles via time-gated mid-infrared photothermal microscopy

The transient dynamics of photothermal signals provide interesting insights into material properties and heat diffusion. In a mid-infrared (mid-IR) photothermal microscope, the imaging contrast in a standard amplitude imaging can decrease due to thermal diffusion effects. It is shown that contrast varies for poly-methyl 2-methylpropenoate (PMMA) particles of different sizes when embedded in an absorbing medium of water (H2O) based on levels of heat exchange under the water absorption resonance. Using time-resolved boxcar (BC) detection, analysis of the transient thermal dynamics at the bead-water interface is presented, and the time decay parameters for 500 nm and 100 nm beads are determined. Enhanced (negative) imaging contrast is observed for less heat exchange between the water and bead, as in the case for the 100 nm bead. For the 500 nm bead, boxcar imaging before heat exchange starts occurring, leads to an increase of the imaging contrast up to a factor of 1.6.

Multifunctional Acrylic Polymers with Enhanced Adhesive Property Serving as Excellent Edge Encapsulant for Stable Optoelectronic Devices

Pendant groups in acrylic adhesive polymers (Ads) have a profound influence on adhesive and cohesive properties and additionally on encapsulant application. However, a systematic investigation to assess the impact of the pendant groups' length and bulkiness is rare, and there is not even a single report on applying Ads as interfacial adhesion promotors and encapsulation materials simultaneously. Herein, we have developed a series of multifunctional methacrylic polymers, namely, R-co-Ads, with varying pendant length and bulkiness (R = methyl (C1), ethyl (C2), propyl (C3), butyl (C4), pentyl (C5), hexyl (C6), isobutyl (iC4), and 2-ethylhexyl (2EH)). The adhesion-related experimental results reveal that R-co-Ads have high transparency, strong adhesion strength to the various contact surfaces, and a fast cure speed. In particular, C1-co-Ad shows a superior adhesion performance with an improved cross-cut index of 4B and a shear bonding strength of 1.56 MPa. We also have adopted C1-co-Ad for encapsulation of various emerging optoelectronic applications (e.g., perovskite solar cell-, charge transport-, and conductivity-related characteristics), demonstrating its excellent edge encapsulant served to improve the device stability against ambient air conditions. Our study establishes the structure-adhesion-surface relationships, advancing the better design of adhesives and encapsulants for various research fields.

Local Dynamics of the Hydration Water and Poly(Methyl Methacrylate) Chains in PMMA Networks

The dynamic behavior of water molecules and polymer chains in a hydrated poly(methyl methacrylate) (PMMA) matrix containing a small amount of water molecules was investigated. Water molecules have been widely recognized as plasticizers for activating the segmental motion of polymer chains owing to their ability to reduce the glass transition temperature. In this study, combined with judicious hydrogen/deuterium labeling, we conducted quasi-elastic neutron scattering (QENS) experiments on PMMA for its dry and hydrated states. Our results clearly indicate that the dynamics of hydrated polymer chains are accelerated, and that individual water molecules are slower than bulk water. It is therefore suggested that the hydration water affects the local motion of PMMA and activates the local relaxation process known as restricted rotation, which is widely accepted to be generally insensitive to changes in the microenvironment.

Tunable Anion Exchange Membrane Conductivity and Permselectivity via Non-Covalent, Hydrogen Bond Cross-Linking

Ion exchange membranes (IEMs) are a key component of electrochemical processes that purify water, generate clean energy, and treat waste. Most conventional polymer IEMs are covalently cross-linked, which results in a challenging tradeoff relationship between two desirable properties─high permselectivity and high conductivity─in which one property cannot be changed without negatively affecting the other. In an attempt to overcome this limitation, in this work we synthesized a series of anion exchange membranes containing non-covalent cross-links formed by a hydrogen bond donor (methacrylic acid) and a hydrogen bond acceptor (dimethylacrylamide). We show that these monomers act synergistically to improve both membrane permselectivity and conductivity relative to a control membrane without non-covalent cross-links. Furthermore, we show that the hydrogen bond donor and acceptor loading can be used to tune permselectivity and conductivity relatively independently of one another, escaping the tradeoff observed in conventional membranes.

Heterogeneous Bonding of PMMA and Double-Sided Polished Silicon Wafers through H2O Plasma Treatment for Microfluidic Devices

In this work we report on a rapid, easy-to-operate, lossless, room temperature heterogeneous H2O plasma treatment process for the bonding of poly(methyl methacrylate) (PMMA) and double-sided polished (DSP) silicon substrates by for utilization in sandwich structured microfluidic devices. The heterogeneous bonding of the sandwich structure produced by the H2O plasma is analyzed, and the effect of heterogeneous bonding of free radicals and high charge electrons (e−) in the formed plasma which causes a passivation phenomenon during the bonding process investigated. The PMMA and silicon surface treatments were performed at a constant radio frequency (RF) power and H2O flow rate. Changing plasma treatment time and powers for both processes were investigated during the experiments. The gas flow rate was controlled to cause ionization of plasma and the dissociation of water vapor from hydrogen (H) atoms and hydroxyl (OH) bonds, as confirmed by optical emission spectroscopy (OES). The OES results show the relative intensity peaks emitted by the OH radicals, H and oxygen (O). The free energy is proportional to the plasma treatment power and gas flow rate with H bonds forming between the adsorbed H2O and OH groups. The gas density generated saturated bonds at the interface, and the discharge energy that strengthened the OH-e− bonds. This method provides an ideal heterogeneous bonding technique which can be used to manufacture new types of microfluidic devices.

Structure and dynamics of poly(methacrylic acid) and its interpolymer complex probed by covalently bound rhodamine-123

The dynamics and structural characteristics of polymethacrylic acid bound rhodamine-123 (PMAA-R123) and its interpolymer complex formed through hydrogen bonding between the monomeric units with poly(vinylpyrrolidone) were investigated using single molecular fluorescence studies. The time resolved fluorescence anisotropy decay of PMAA-R123 under acidic pH exhibits an associated anisotropy decay behavior characteristic of two different environments experienced by the fluorophore with one shorter and another longer rotational correlation time. The anisotropy decay retains normal bi-exponential behavior under neutral pH. Fluorescence correlation spectroscopic investigation reveals that the attached fluorophore undergoes hydrolysis under basic condition which results in the release of the fluorophore from the polymer backbone. Shrinkage in the hydrodynamic radius of PMAA is observed on addition of the complementary polymer PVP which is attributed to the formation compact solubilized nanoparticle like aggregates. The size of particle further decreases on the addition of NaCl. The detailed results show that these complexes have potential for use as drug-delivery system under physiological conditions.

Self-Assembly of Large Magnetic Nanoparticles in Ultrahigh Molecular Weight Linear Diblock Copolymer Films

The development of diblock copolymer (DBC) nanocomposite films containing magnetic nanoparticles (NPs) with diameters (D) over 20 nm is a challenging task. To host large iron oxide NPs (Fe₃O₄, D = 27 ± 0.6 nm), an ultrahigh molecular weight (UHMW) linear DBC polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) is used as a template in the present work. Due to hydrogen bonding between the carboxylic acid ligands of the NPs and the ester groups in PMMA, the NPs show an affinity to the PMMA block. The localization of the NPs inside the DBC is investigated as a function of the NP concentration. At low NP concentrations, NPs are located preferentially at the interface between PS and PMMA domains to minimize the interfacial tension caused by the strong segregation strength of the UHMW DBC. At high NP concentrations (≥10 wt %), chain-like NP aggregates (a head-to-tail orientation) are observed in the PMMA domains, resulting in a change of the morphology from sphere to ellipsoid for part of the PMMA domains. Magnetic properties of the hybrid films are probed via superconducting quantum interference device magnetometry. All hybrid films show ferrimagnetism and are promising for potential applications in magnetic data storage.

Effect of external electric field on nanobubbles at the surface of hydrophobic particles during air flotation

In this paper, the effect of external electric field on nanobubbles adsorbed on the surface of hydrophobic particles during air flotation was studied by molecular dynamics simulations. The gas density distribution, diffusion coefficient, viscosity, and the change of the angle and number distribution of hydrogen bonds in the system with different amounts of gas molecules were calculated and compared with the results without an external electric field. The results show that the external electric field can make the size of the bubbles smaller. The diffusion coefficient of the gas increases and the viscosity of the system decreases when the external electric field is applied, which contribute to the reduction of the size of the nanobubbles. At the same time, comparing with the results under no external electric field, the angle of hydrogen bonding under the external electric field will increase, and the proportion of water molecules containing more hydrogen bonds will reduce, which further explains the reason why the external electric field reduces the viscosity. The conclusions of this paper demonstrate at the micro level that the external electric field can enhance the efficiency of air-floating technology for the separation of hydrophobic particles, which may provide meaningful theoretical guidance for the application and optimization of electric field-enhanced air-floating technology in practice.

Vapor-Phase Nanopatterning of Aminosilanes with Electron Beam Lithography: Understanding and Minimizing Background Functionalization

Electron beam lithography (EBL) is a highly precise, serial method for patterning surfaces. Positive tone EBL resists enable patterned exposure of the underlying surface, which can be subsequently functionalized for the application of interest. In the case of widely used native oxide-capped silicon surfaces, coupling an activated silane with electron beam lithography would enable nanoscale chemical patterning of the exposed regions. Aminoalkoxysilanes are extremely useful due to their reactive amino functionality but have seen little attention for nanopatterning silicon surfaces with an EBL resist due to background contamination. In this work, we investigated three commercial positive tone EBL resists, PMMA (950k and 495k) and ZEP520A (57k), as templates for vapor-phase patterning of two commonly used aminoalkoxysilanes, 3-aminopropyltrimethoxysilane (APTMS) and 3-aminopropyldiisopropylethoxysilane (APDIPES). The PMMA resists were susceptible to significant background reaction within unpatterned areas, a problem that was particularly acute with APTMS. On the other hand, with both APTMS and APDIPES exposure, unpatterned regions of silicon covered by the ZEP520A resist emerged pristine, as shown both with SEM images of the surfaces of the underlying silicon and through the lack of electrostatically driven binding of negatively charged gold nanoparticles. The ZEP520A resist allowed for the highly selective deposition of these alkoxyaminosilanes in the exposed areas, leaving the unpatterned areas clean, a claim also supported by contact angle measurements with four probe liquids and X-ray photoelectron spectroscopy (XPS). We investigated the mechanistic reasons for the stark contrast between the PMMA resists and ZEP520A, and it was found that the efficacy of resist removal appeared to be the critical factor in reducing the background functionalization. Differences in the molecular weight of the PMMA resists and the resulting influence on APTMS diffusion through the resist films are unlikely to have a significant impact. Area-selective nanopatterning of 15 nm gold nanoparticles using the ZEP520A resist was demonstrated, with no observable background conjugation noted in the unexposed areas on the silicon surface by SEM.

Hydrogen bond directed surface dynamics at tactic poly(methyl methacrylate)/water interface

The complexity of induced ordering for tactic poly(methyl methacrylate) (PMMA) thin films in contact with water is examined through all-atom molecular dynamics with validated potentials. We observe that for the water molecules that are hydrogen bonded to the PMMA surface, the isotactic and atactic PMMA show a 33% longer relaxation time compared to syndiotactic PMMA. Almost 94% of hydrogen bonds are with the carbonyl groups of PMMA, irrespective of temperature and tacticity. The stability in re-orientation and nature of hydrogen bond participation for the carbonyl groups as well as about 20% higher interaction energies of carbonyl group hydrogen bonded with water for atactic form indicates existence of cooperative effects. Quantifying the dynamics of hydrogen bond at the tactic interface is important in understanding the role tacticity plays in controlling adhesion and biocompatibility, a design choice that has been gaining ground in the soft material science community.

pH-Induced Association and Dissociation of Intermolecular Complexes Formed by Hydrogen Bonding between Diblock Copolymers

Poly(sodium styrenesulfonate)⁻block⁻poly(acrylic acid) (PNaSS⁻b⁻PAA) and poly(sodium styrenesulfonate)⁻block⁻poly(N-isopropylacrylamide) (PNaSS⁻b⁻PNIPAM) were prepared via reversible addition⁻fragmentation chain transfer (RAFT) radical polymerization using a PNaSS-based macro-chain transfer agent. The molecular weight distributions (Mw/Mn) of PNaSS⁻b⁻PAA and PNaSS⁻b⁻PNIPAM were 1.18 and 1.39, respectively, suggesting that these polymers have controlled structures. When aqueous solutions of PNaSS⁻b⁻PAA and PNaSS⁻b⁻PNIPAM were mixed under acidic conditions, water-soluble PNaSS⁻b⁻PAA/PNaSS⁻b⁻PNIPAM complexes were formed as a result of hydrogen bonding interactions between the pendant carboxylic acids in the PAA block and the pendant amide groups in the PNIPAM block. The complex was characterized by ¹H NMR, dynamic light scattering, static light scattering, and transmission electron microscope measurements. The light scattering intensity of the complex depended on the mixing ratio of PNaSS⁻b⁻PAA and PNaSS⁻b⁻PNIPAM. When the molar ratio of the N-isopropylacrylamide (NIPAM) and acrylic acid (AA) units was near unity, the light scattering intensity reached a maximum, indicating stoichiometric complex formation. The complex dissociated at a pH higher than 4.0 because the hydrogen bonding interactions disappeared due to deprotonation of the pendant carboxylic acids in the PAA block.

Static and Dynamic Water Motion-Induced Instability in Oxide Thin-Film Transistors and Its Suppression by Using Low-k Fluoropolymer Passivation

Here, we report static and dynamic water motion-induced instability in indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs) and its effective suppression with the use of a simple, solution-processed low-k (ε ∼ 1.9) fluoroplastic resin (FPR) passivation layer. The liquid-contact electrification effect, in which an undesirable drain current modulation is induced by a dynamic motion of a charged liquid such as water, can cause a significant instability in IGZO TFTs. It was found that by adopting a thin (∼44 nm) FPR passivation layer for IGZO TFTs, the current modulation induced by the water-contact electrification was greatly reduced in both off- and on-states of the device. In addition, the FPR-passivated IGZO TFTs exhibited an excellent stability to static water exposure (a threshold voltage shift of +0.8 V upon 3600 s of water soaking), which is attributed to the hydrophobicity of the FPR passivation layer. Here, we discuss the origin of the current instability caused by the liquid-contact electrification as well as various static and dynamic stability tests for IGZO TFTs. On the basis of our findings, we believe that the use of a thin, solution-processed FPR passivation layer is effective in suppressing the static and dynamic water motion-induced instabilities, which may enable the realization of high-performance and environment-stable oxide TFTs for emerging wearable and skin-like electronics.

Molecular dynamics simulation for the impact of an electrostatic field and impurity Mg2+ions on hard water

A detailed analysis of the structural parameters and dynamic parameters of hard water solutions under an external electrostatic field was performed by molecular dynamics (MD) simulations with the presence of impurity Mg²⁺ions.

Molecular structure of poly(methyl methacrylate) surface II: Effect of stereoregularity examined through all-atom molecular dynamics

Utilizing all-atom molecular dynamics (MD), we have analyzed the effect of tacticity and temperature on the surface structure of poly(methyl methacrylate) (PMMA) at the polymer-vacuum interface. We quantify these effects primarily through orientation, measured as the tilt with respect to the surface normal, and the surface number densities of the α-methyl, ester-methyl, carbonyl, and backbone methylene groups. Molecular structure on the surface is a complex interplay between orientation and number densities and is challenging to capture through sum frequency generation (SFG) spectroscopy alone. Independent quantification of the number density and orientation of chemical groups through all-atom MD presents a comprehensive model of stereoregular PMMA on the surface. SFG analysis presented in part I of this joint publication measures the orientation of molecules that are in agreement with MD results. We observe the ester-methyl groups as preferentially oriented, irrespective of tacticity, followed by the α-methyl and carbonyl groups. SFG spectroscopy also points to ester-methyl being dominant on the surface. The backbone methylene groups show a very broad angular distribution, centered along the surface plane. The surface number density ratios of ester-methyl to α-methyl groups show syndiotactic PMMA having the lowest value. Isotactic PMMA has the highest ratios of ester- to α-methyl. These subtle trends in the relative angular orientation and number densities that influence the variation of surface structure with tacticity are highlighted in this article. A more planar conformation of the syndiotactic PMMA along the surface (x-y plane) can be visualized through the trajectories from all-atom MD. Results from conformation tensor calculations for chains with any of their segments contributing to the surface validate the visual observation.

Adhesion and friction properties of polymer brushes: fluoro versus nonfluoro polymer brushes at varying thickness

A series of different thicknesses of fluoro poly(2,2,2-trifluoroethyl methacrylate) and its analogous nonfluoro poly(ethyl methacrylate) polymer brushes were prepared via surface-initiated ATRP (SI-ATRP) on Si(111) surfaces. The thiol-yne click reaction was used to immobilize the SI-ATRP initiator with a high surface coverage, in order to achieve denser polymer brushes (grafting density from ~0.1 to 0.8 chains/nm(2)). All polymer brushes were characterized by static water contact angle measurements, infrared absorption reflection spectroscopy, and X-ray photoelectron spectroscopy. Adhesion and friction force measurements were conducted with silica colloidal probe atomic force microscopy (CP-AFM) under ambient and dry (argon) conditions. The fluoro poly(2,2,2-trifluoroethyl methacrylate) polymer showed a decrease in adhesion and friction with increasing thickness. The analogous nonfluoro poly(ethyl methacrylate) polymer brushes showed high adhesion and friction under ambient conditions. Friction coefficients down to 0.0057 (ambient conditions) and 0.0031 (dry argon) were obtained for poly(2,2,2-trifluoroethyl methacrylate) polymer brushes with 140 nm thickness, which are the lowest among these types of polymer brushes.

Effect of side-chain carbonyl groups on the interface of vinyl polymers with water

The nature of the polymer-water interface in the poly(methyl 2-propenyl ether) (PMPE)-water model system is investigated by sum-frequency generation spectroscopy, which at the moment gives the best depth resolution among available techniques. PMPE, synthesized via living cationic polymerization, is structurally similar to poly(methyl methacrylate) (PMMA) except for lacking a carbonyl group. We here probe the polymer local conformation as well as the aggregation states of water at the interface. Comparing the results of our measurements to the PMMA-water system, the effect of a carbonyl group on the water structure at the interface is discussed. This knowledge should be crucial to the design and construction of highly functionalized polymer interfaces for bioapplications.