Scratching behavior of elastomeric poly(dimethylsiloxane) coatings

Scratch testing has been performed on elastomeric poly(dimethylsiloxane) (PDMS) coatings on stainless steel with a spherical indenter. The friction coefficient (horizontal‐to‐normal force ratio) during scratching decreases with increasing normal load. This result can be explained by assuming that during scratching the contact area is determined by elastic deformation and the horizontal force is proportional to the contact area. With increasing driving speed, the friction coefficient increases, but the rate of increase decreases; this suggests that the scratching of the PDMS coating is a rate process and that the viscoelastic property of the coating influences its frictional behavior. Below a critical normal load, which increases with the coating thickness, the PDMS coating recovers elastically after being scratched so that there are no scratch marks left behind. Above the critical normal load, the coating is damaged by a combination of delamination at the coating/substrate interface and through‐thickness cracking. When the coating is damaged, there is an increase in the friction coefficient, and the friction force displays significant fluctuations. Furthermore, the critical normal load increases with the driving speed; this implies that time is needed to nucleate damage. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1530–1537, 2002     

Synthesis and characterization of multiblock copolyesters containing poly(dimethylsiloxane) in the soft segments

Synthesis and thermal properties of poly(aliphatic/aromatic-ester) copolymers containing additionally poly(dimethylsiloxane) (PDMS) chains in the soft segments are discussed. A two step method of transesterification and polycondensation from the melt was carried out in a presence of magnesium-titanate catalyst. An aliphatic dimer fatty acid was used as a component of the soft segments while poly(butylene terephthalate) (PBT) constituted the hard blocks. Effectiveness of the incorporation of PDMS into polymer chain was confirmed by the Soxhlet extraction and infrared spectroscopy of an excess of 1,4-butane diol destilled off from the polycondensation reaction. Multiblock copolymers showed microphase separation as determined by differential scanning calorimetry. Incorporation of a small amount of PDMS (up to 14.5 wt.-%) into polymer chain containg low concentration of hard segments of PBT lead to decrease in crystallinity of such copolymers. This may indicate that semicrystalline PBT are dissolved in the amorphous matrix of the soft segments.     

Vibrational spectroscopic study of poly(dimethylsiloxane)-ZnO nanocomposites

A series of poly(dimethylsiloxane)-zinc oxide (PDMS-ZnO) nanocomposites having different concentrations of ZnO nanoparticles (0, 1, 5, 10 and 20 wt%) have been prepared. Raman and FTIR-ATR spectroscopic analysis was performed in order to determine the interaction between the ZnO nanoparticles and PDMS polymer matrix. Density functional theory (DFT) using the (B3-LYP)/6-311++G(2df,2p) method was used to investigate the vibrational spectra of PDMS. A complete vibrational assignment is supported by the normal coordinate analysis, calculated Raman activities as well as IR intensities.The presence of ZnO nanoparticles in PDMS gives rise to significant differences in relative intensities of the characteristic vibrational bands with respect to the cross-linked polymer. The changes in relative intensities of Raman bands, as well as swelling measurements, were used to explain the effect of ZnO nanoparticles on the cross-linked structure of PDMS nanocomposites. It is established that ZnO nanoparticles influence the cross-linking density of the polymer matrix.     

Differential scanning calorimetry (DSC) and Raman spectroscopy study of poly(dimethylsiloxane)

Poly(dimethylsiloxane) was studied by laser Raman spectroscopy and differential scanning calorimetry. The Si O Si skeletal mode at 489 cm⁻¹ and the C Si C deformation bands at 188 cm⁻¹ and 158 cm⁻¹ were studied as functions of temperature from ambient to −130°C, and effects of temperature interpreted in accordance with results from thermal analysis. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2805–2810, 1998     

Stability of filled poly(dimethylsiloxane) and poly(diphenylsiloxane-co-dimethylsiloxane) elastomers to cyclic stress at elevated temperature

The response of aluminum oxide-filled poly(dimethyl siloxane) and poly(diphenylsiloxane-co-dimethylsiloxane) elastomers, containing 3–24 mol % diphenylsiloxane, to cyclic stress at elevated temperatures (dynamic creep) was evaluated. The materials could be divided into two classes, based on their response to the application of cyclic stress: no or low-diphenylsiloxane content elastomers in which substantial creep and a decrease in crosslink density were observed, and high diphenylsiloxane content (16–24 mol %) elastomers that showed decreased creep with increasing diphenylsiloxane content and an increase in crosslink density. It was suggested that the phenyl groups stabilize the siloxane bond in the polymer backbone, decreasing the rate of chain scission reactions as the diphenylsiloxane content increases and stabilizing the elastomer against creep. The balance of chain scission, chemical crosslinking, and cyclic formation reactions varies depending on diphenylsiloxane content, giving rise to the differences in dynamic creep behavior. An activation energy of 12.9 kcal/mol was measured for dynamic creep of poly(16% diphenylsiloxane/84% dimethyl siloxane), suggesting that a catalyzed degradation mechanism was responsible. The primary catalysts of the degradation reactions are postulated to be the filler particles. © 1996 John Wiley & Sons, Inc.     

Investigation of adhesion hysteresis in poly(dimethylsiloxane) networks using the JKR technique

The JKR technique was used to determine the source and nature of the adhesion hysteresis present in modified poly(dimethylsiloxane) (PDMS) networks. As controlled excess amounts of the tetrafunctional crosslinker were added to the networks, the adhesion hysteresis increased. It was found that by poisoning the catalyst with a thiol the hysteresis could be significantly lowered, and completely removed in some cases. We believe that the adhesion hysteresis in this system stems from a complexation between the excess crosslinker and the catalyst. We found that the work of adhesion in this case is a function of the unloading rate. The unloading rate dependence of this chemical adhesion hysteresis was attributed to the rate of bond dissociation. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2129–2139, 1998     

Gas sorption,diffusion, and permeation in poly(dimethylsiloxane)

The permeability of poly(dimethylsiloxane) [PDMS] to H₂, O₂, N₂, CO₂, CH₄, C₂H₆, C₃H₈, CF₄, C₂F₆, and C₃F₈, and solubility of these penetrants were determined as a function of pressure at 35 °C. Permeability coefficients of perfluorinated penetrants (CF₄, C₂F₆, and C₃F₈) are approximately an order of magnitude lower than those of their hydrocarbon analogs (CH₄, C₂H₆, and C₃H₈), and the perfluorocarbon permeabilities are significantly lower than even permanent gas permeability coefficients. This result is ascribed to very low perfluorocarbon solubilities in hydrocarbon‐based PDMS coupled with low diffusion coefficients relative to those of their hydrocarbon analogs. The perfluorocarbons are sparingly soluble in PDMS and exhibit linear sorption isotherms. The Flory–Huggins interaction parameters for perfluorocarbon penetrants are substantially greater than those of their hydrocarbon analogs, indicating less favorable energetics of mixing perfluorocarbons with PDMS. Based on the sorption results and conventional lattice solution theory with a coordination number of 10, the formation of a single C₃F₈/PDMS segment pair requires 460 J/mol more energy than the formation of a C₃H₈/PDMS pair. A breakdown in the geometric mean approximation of the interaction energy between fluorocarbons and hydrocarbons was observed. These results are consistent with the solubility behavior of hydrocarbon–fluorocarbon liquid mixtures and hydrocarbon and fluorocarbon gas solubility in hydrocarbon liquids. From the permeability and sorption data, diffusion coefficients were determined as a function of penetrant concentration. Perfluorocarbon diffusion coefficients are lower than those of their hydrocarbon analogs, consistent with the larger size of the fluorocarbons. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 415–434, 2000     

Molecular mobility of free‐radical‐functionalized carbon‐nanotube/siloxane/poly(urea urethane) nanocomposites

Multiwalled carbon nanotubes (MWNTs) were functionalized by a free‐radical reaction of vinyltriethoxysilane and were blended with poly(urea urethane) (PUU) containing poly(dimethylsiloxane) as a soft segment. PUU was end‐capped with aminopropyltriethoxysilane (A‐silane) or phenyltriethoxysilane (P‐silane).A‐silane‐end‐capped PUU was covalently bonded to functionalized MWNTs, whereas P‐silane‐end‐capped PUU was noncovalently bonded to pristine MWNTs by a π–π interaction. Fourier transform infrared, Raman spectra, and thermogravimetric analysis confirmed the functionalization of MWNTs. The results showed that the optimal reaction time of the functionalization of MWNT was 8 h, and the organic content of the modified carbon nanotubes reached 35.22%. Solid‐state nuclear magnetic resonance and dynamic mechanical analysis were used to investigate the molecular structure and molecular mobility of the carbon‐nanotube/PUU nanocomposites. A‐silane PUU covalently bonded to MWNTs showed a considerable reduction in the molecular motion of the soft segment, which led to the glass‐transition temperature decreasing from ?117 to ?127 °C as MWNTs were incorporated. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6084–6094, 2005     

Library synthesis and characterization of 3‐aminopropyl‐terminated poly(dimethylsiloxane)s and poly(ϵ‐caprolactone)‐b‐poly(dimethylsiloxane)s

Libraries of 3‐aminopropyl‐terminated poly(dimethylsiloxane) (APT–PDMS) and poly(?‐caprolactone)–poly(dimethylsiloxane)–poly(?‐caprolactone) (PCL—PDMS–PCL) triblock copolymers were synthesized. Preliminary experiments were carried out to select an appropriate catalyst and route for the poly(dimethylsiloxane) synthesis, and trial experiments were conducted to verify the successful synthesis of the intended polymer compositions. Then, a series of APT–PDMS oligomers were synthesized with an automated combinatorial high‐throughput synthesis system to cover a molecular weight range of 2500–50,000 g/mol. Trial PCL—PDMS–PCL triblock copolymers were synthesized with the automated reactor system and characterized in detail with rapid gel permeation chromatography, high‐throughput Fourier transform infrared, nuclear magnetic resonance, and differential scanning calorimetry. Finally, two library synthesis experiments were carried out in which the lengths of both the poly(dimethylsiloxane) and poly(?‐caprolactone) blocks in the PCL—PDMS–PCL triblock copolymers were varied. The results obtained from these experiments demonstrated that it was possible to synthesize libraries of well‐defined APT–PDMS oligomers and PCL—PDMS–PCL triblock copolymers with an automated high‐throughput system. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4880–4894, 2006     

Area‐selective microwrinkle formation on poly(dimethylsiloxane) by treatment with strong acid

Microwrinkles were formed by treating poly(dimethylsiloxane) (PDMS) surfaces with a mixture of concentrated sulfuric acid and nitric acid at 80 °C followed by a water rinsing step. The acid treatment oxidized the treated area, which also swelled owing to absorption of water during the rinsing step. This absorption of water induced a compressive stress on the PDMS surface that caused the formation of wrinkles. The appearance of wrinkles was controlled by the time interval between the end of the acid treatment and the beginning of the water rinsing step. Wrinkles were formed when the time interval was shorter than 5 s, as water was absorbed by the hygroscopic acid molecules within the treated surface. For longer time intervals of 300 s, this phenomenon was not observed. Based on these findings, a procedure for forming wrinkles in specific areas was developed by hydrating the chosen areas with wet filter paper cut into specific shapes after the acid treatment. The formation of wrinkles was confined to the area under the piece of paper. The orientation and alignment of the wrinkles at the boundaries were also characterized. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 167–174     

Synthesis,structure, and properties of hybrid organic–inorganic composites based on polysiloxanes. II. Comparisons between poly(methylphenylsiloxane) and poly(dimethylsiloxane), and between titania and silica

The work reported in the preceding article in this series is extended by consideration of polysiloxane–ceramic composites based on atactic poly(methylphenylsiloxane) (PMPS) elastomers instead of poly(dimethylsiloxane). The former is noncrystallizable because of its stereochemically irregular structure, while the latter is crystallizable. In addition, some composites were prepared by the in situ precipitation of titania instead of silica. The resulting materials were characterized using differential scanning calorimetry, equilibrium stress–strain measurements in elongation, small-angle neutron scattering, and transmission electron microscopy. The moduli of the PMPS elastomers were found to increase significantly with increase in amount of either type of filler, with reinforcing upturns at high elongation in the case of the silica. Because the PMPS elastomers were amorphous, it is obvious that strain-induced crystallization is not required for these upturns in modulus. Titania did not give as good reinforcement as did silica, at least in the case of PMPS. Differences in interactions between the polymer and the two fillers are obviously important in this regard, but differences in particle morphology probably also contribute. Specifically, the titania “particles” were significantly larger than the silica particles when observed in TEM, and appeared to be much more porous. The actual domain size as measured by scattering, however, was only approximately 5% larger. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1191–1200, 1998     

Simple poly(dimethylsiloxane) surface modification to control cell adhesion

Poly(dimethylsiloxane) (PDMS) has a long history of exploitation in a variety of biological and medical applications. Particularly in the past decade, PDMS has attracted interest as a material for the fabrication of microfluidic biochip. The control of cell adhesion on a PDMS surface is important in many microfluidic applications such as cell culture or cell‐based chemicals/drug testing. Unlike many complicated approaches, this study reports simple methods of PDMS surface modification to effectively inhibit or conversely enhance cell adhesion on a PDMS surface using Pluronic surfactant solution and poly‐L ‐lysine, respectively. This research basically succeeded our prior work to further confirm the long‐term capability of 3% Pluronic F68 surfactant to suppress cell adhesion on a PDMS surface over a 6‐day cell culture. Microscopic observation showed that the treated PDMS surface created an unfavorable interface, where chondrocytes seemed to clump together on day 2 and 6 after chondrocyte seeding, and there was no sign of chondrocyte spreading. On the opposite side, results demonstrated that the poly‐L ‐lysine‐treated surface significantly increased fibroblast adhesion by 32% in contrast to the untreated PDMS, which is comparable to the commercial cell‐culture‐grade microplate. However, fibronectin treatment did not have such an effect. All these fundamental information is found useful for any PDMS‐related application. Copyright © 2008 John Wiley & Sons, Ltd.     

Reversible gelation of poly(dimethylsiloxane) with ionic and hydrogen‐bonding substituents

Poly(dimethylsiloxane) copolymers containing a small fraction of carboxylic acid or Zn‐carboxylate groups were prepared and compared regarding reversible gelation by hydrogen‐bonding and ion‐pair interaction. The polymers were synthesized by condensation of a t‐butylcarboxylate functionalized dichlorosilane with an α,ω‐dihydroxy‐poly(dimethylsiloxane), followed by thermal cleavage of the ester bond. Neutralization of the resulting carboxylic acid substituents was achieved by addition of Zn (acac)₂. Reversible crosslinking was investigated by step stress and oscillating shear experiments. The carboxylic acid containing poly(dimethylsiloxane) became rubberlike upon increasing the temperature and liquified again when it was brought back to room temperature. This observation has been explained tentatively by segregation of the carboxylic acid groups into polar domains at high temperatures [i.e., a behavior like it is observed for systems with a lower critical solution temperature (LCST)]. At ambient temperature, the carboxylic acid groups undergo hydrogen bonding to the Si–O–Si backbone. Clustering of the carboxylic acid groups occurs only as these hydrogen bonds break upon raising temperature. Moisture was found to have a strong influence on the reversal of the crosslinking. Addition of zinc acetylacetonate resulted in the formation of an elastic network already at ambient conditions consistent with the concept of ionomers which undergo reversible gelation by formation of ion‐pair multiplets and clusters in the hydrophobic polymer matrix in particularly at low temperatures. At high temperature, both the carboxylic acid and the carboxylate sample exhibited a rather similar viscoelastic behavior consistent with a common structure where transient crosslinks are formed by clusters of the carboxylic acid and the carboxylate groups. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 485–495, 1999     

Preparation and characterization of epoxy/SiO2 nanocomposites by cationic photopolymerization and sol–gel process

Epoxy/SiO₂ nanocomposite materials were prepared by cationic photopolymerization and sol–gel process using a novel epoxy oligomer (EP‐Si(OC₂H₅)₃) prepared by 3‐isocyanatopropyltriethoxysilane (IPTS)‐grafted bisphenol A epoxy resin and tetraethyl orthosilicate as inorganic precursor. The chemical structures of EP‐Si(OC₂H₅)₃ were characterized by Fourier transformed infrared spectroscopy. Transmission electron microscopy showed that the in situ generated nano‐SiO₂ dispersed uniformly in the EP matrix, and its average diameter is around 40 nm. The relationship between nanocomposite materials' thermal/mechanical properties and nano‐SiO₂ introduced were studied by thermogravimetric analysis, dynamic mechanical analysis, and impact strength test. The results showed that the nanocomposite materials' thermal and mechanical properties improved a lot with increase of the SiO₂ content. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis,characterization, and antimicrobial activity of some novel poly(ether ketone)s

Low molecular weight poly(ether ketone)s were synthesized from phenol, 1,4‐phenylenedioxy diacetylchloride, chloroacetylchloride, and dichloroalkanes [1,2‐dichloroethane and dichloromethane] by a Friedel–Crafts reaction with anhydrous aluminum chloride as a catalyst and carbon disulfide as a solvent. The conditions for the preparation of the poly(ether ketone)s and the chlorine contents obtained with the Carius method were examined, and a reaction scheme for each resin was established. The molecular weights and polydispersities of the resins were obtained by gel permeation chromatography. The polyketones were characterized by IR spectroscopy. The characteristic frequencies due to different functional groups were assigned. The thermal properties of the resins were studied with thermogravimetry and differential scanning calorimetry. The characteristic temperatures of thermal degradation for the poly(ether ketone)s were evaluated with thermogravimetric analysis. The kinetic parameters for the decomposition reactions of the resins were obtained with Broido and Doyle's method, and the heats of fusion were obtained from differential scanning calorimetry thermograms. The polyketones were thermally stable up to 200 °C. All the polyketones were tested for their microbial properties against bacteria, fungi, and yeast. The effect of poly(ether ketone)s on the growth of these microorganisms was investigated, and the polyketones were found to inhibit the growth of the microorganisms to a considerable extent. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2335–2344, 2003     

Synthesis of poly(vinylidene fluoride) (PVdF)/silica hybrids having interpenetrating polymer network structure by using crystallization between PVdF chains

High transparent and homogeneous poly(vinylidene fluoride) (PVdF)/silica hybrids were obtained by using an in‐situ interpenetrating polymer network (IPN) method. The simultaneous formation of PVdF gel resulting from the physical cross‐linking and silica gel from sol–gel process prevented the aggregation of PVdF in silica gel matrix. To form the physical cross‐linking between PVdF chains, the cosolvent system of dimethylformaide (DMF) and γ‐butyrolactone was used. The obtained PVdF/silica hybrids had an entangled combination of physical PVdF gel and silica gel, which was called a “complete‐ IPN” structure. The physical cross‐linking between PVdF chains in silica gel matrix was confirmed by differential scanning calorimetry (DSC) measurements. The miscibility between PVdF and silica phase was examined by scanning electron microscopy (SEM) and tapping mode atomic force microscopy (TM‐AFM) measurements. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3543–3550, 2005     

Preparation and properties of poly(styrene-co-maleic anhydride)/silica hybrid materials by the in situ sol–gel process

Poly(styrene-co-maleic anhydride)/silica hybrid material has been successfully prepared from styrene–maleic anhydride copolymer and tetraethoxysilane (TEOS) in the presence of a coupling agent (3-aminopropyl)triethoxysilane (APTES) by an in situ sol–gel process. It was observed that the gel time of sol–gel solution was dramatically influenced by the amount of APTES. The hybrid material exhibits optical transparency almost as good as both silica gel and the copolymer. The covalent bonds between organic and inorganic phases were introduced by the aminolysis reaction of the amino group with maleic anhydride units of copolymer to form a copolymer bearing trimethoxysilyl groups, which undergo hydrolytic polycondensation with TEOS. The differential scanning calorimetry (DSC) showed that the glass transition temperature of the hybrid materials increases with increasing of SiO₂ composition. Photographs of scanning electron microscopy (SEM) and atomic force microscopy (AFM) inferred that the size of the inorganic particles in the hybrid materials was less than 20 nm. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1607–1613, 1998