Cross-linked Siloxane Research Articles

Synthesis and Characterization of Durable Antifog Silane-Pyrrolidone Thin Coatings onto Polymeric Films.

The fogging of transparent surfaces-condensation of water vapor in the air to a small liquid surface at specific environmental conditions-scatters incident light, creating a blurry vision. Fogging presents a significant challenge in various industries, adversely affecting numerous applications including plastic packaging, agricultural films, and various optical devices. Superhydrophobic or superhydrophilic coatings are the main strategies used to induce antifogging to minimize light scattering. Here, an innovative approach is introduced to mitigate fogging by modifying the surface properties of polymeric films, focusing on corona-treated polyethylene as a model. Coatings were prepared in two successive steps: the addition of radical co-polymerization of methacryloxypropyltriethoxysilane and N-vinylpyrrolidone followed by the step-growth Stöber polymerization of the formed silane monomer. The polymeric dispersion was spread on oxidized films via a Mayer rod and dried. Scanning and force microscopy, FIB, XPS, and UV-vis spectroscopy revealed a thin coating composed of cross-linked siloxane (Si-O-Si) covalently bonded to surface hydroxyls exposing pyrrolidone groups. Contact angle measurements, hot-fog examination, and durability tests indicated a durable antifogging activity.

Lipid cubic phase with an organic-inorganic hybrid structure formed by organoalkoxysilane lipid.

A lipid cubic phase encompassing a cross-linked siloxane structure was formed by the self-assembly of a synthetic organoalkoxysilane lipid in water. The spontaneous sol-gel reaction of the alkoxysilane moiety on the lipid head group produced an organic-inorganic hybrid material with a double gyroid Ia3d cubic structure.

A novel strategy to construct hydrogels with anti-swelling and water-retention abilities by covalent surface modification.

Hydrogels have been widely used in various fields due to their diverse properties and flexible preparation methods. However, limited by the open network structure, hydrogels inevitably lose water in air or absorb water in aqueous solution, resulting in the loss of intrinsic functions, which severely hinders their practical applications. To address this issue, a general strategy was developed by subsequently modifying the surface of hydrogels with branched polyethyleneimine (PEI) and (3-(methacryloxy)propyl)trimethoxysilane (MPS) to covalently construct a dense cross-linked siloxane layer on the hydrogel surface. As a proof of concept, poly(2-(dimethylamino)ethyl methacrylate)/sodium alginate (PDMAEMA/SA) hydrogels were chosen as the model hydrogels to verify the feasibility of this strategy. The hydrogels adsorbed PEI to form amino-rich surfaces through hydrogen bonding, followed by covalently grafting MPS through rapid and catalyst-free mutual chemical reactions between acrylates and amine groups, as well as the hydrolysis of MPS. After modification, robust hydrophobic surfaces were successfully fabricated on the hydrophilic hydrogels. The modified hydrogels exhibited extraordinary anti-swelling and water-retention abilities. As the most typical intrinsic properties of hydrogels, the conductivity and sensing performance were well preserved. The strategy reported here provides a new insight into the construction of hydrogels with anti-swelling and water-retention abilities.

Trimethoxy Silyl End-Capped Hyperbranched Polyglycidol/Polycaprolactone Particle Gels for Cell Delivery and Tissue Repair: Mechanical Properties, Biocompatibility, and Biodegradability Studies

This study focuses on the development of new biocompatible and biodegradable particle gel scaffolds based on PCL-HBPG/1SiHBPG triblock copolymers composed of a polycaprolactone (PCL) core and two outer blocks of trimethoxysilyl end-capped hyperbranched polyglycidol (HBPG/1SiHBPG) that have the potential to be used in soft tissue regeneration. The relationship between the gel’s composition, structure, mechanical properties, and performance has been investigated for the first time and the copolymer design parameters have been optimized. The particle gel scaffolds were formed from the concentrated dispersions of the most hydrophobic PCL-45HBPG/1SiHBPG at low temperatures, and were the result of the numerous hydrogen bonds formed from the HBPG/1SiHBPG moieties as well as the formation of siloxane crosslinks (i.e., Si–O–Si bonds). These gels were formed in the physiological temperature range. Gels with a mechanical strength that gradually increases were formed from the physically crosslinked PCL-45HBPG/1SiHBPG particles effectively and safely, in the absence of UV radiation. They feature high elasticity and undergo enzyme-triggered disassembly. The gels are biocompatible and have the potential to invoke cell attachment and differentiation in the absence of exogenous biological stimuli. A successful outcome of this study will be the prospect of a new approach for tissue regeneration that is currently not available.

A Hydrogen-Containing Di-Phenyl Siloxane Cross-Linker for Ultra-High Hardness and High Refractive Index Silicone Resin and its Application in LED Encapsulation

A Hydrogen-Containing Di-Phenyl Siloxane Cross-Linker for Ultra-High Hardness and High Refractive Index Silicone Resin and its Application in LED Encapsulation

Rational fabrication of fluorine-free, superhydrophobic, durable surface by one-step spray method

The role of superhydrophobic coating in metal anti-corrosion, oil leakage treatment, waterproofing and antifouling cannot be overstated, yet the application of conventional superhydrophobic coatings is limited due to their toxicity, poor mechanical stability, and high cost. Herein we report our design on an eco-friendly wax-derived organic-based superhydrophobic coating based on self-designed sol and eco-friendly wax and integrated the spray coating technique. The W-GPAC coating exhibits superhydrophobicity (Contact Angle: 170.6°, Sliding Angle: 5.3°) with a glass substrate. It should be noted that the coating could preserve excellent superhydrophobic property in water spray impact test (Contact Angle:160° after 500 water impact cycles), linear abrasion test(Contact Angle:160° after 120 cm linear abrasion), and acid-base durability test (Contact Angle: greater than 165° after immersion in the acidic or alkaline environment for 600 min). In addition, the coating maintains outstanding adhesion with various substrates even at freezing treatment. The superior performance of the coating comes from the folded structure formed by the drying of GPAC sol which is formed by the dense siloxane crosslinking network of GPAC sol and long-chain silane on the coating surface. Taken together, the W-GPAC superhydrophobic coating enjoys low manufacturing cost, easy degradability, and no secondary pollution, and can be applied to almost commonly used substrates with superior mechanical durability, which could provide alternative solution for superhydrophobic application.

Self-Restructuring of Polyhydromethylsiloxanes by the Hydride Transfer Process: A New Approach to the Cross-Linking of Polysiloxanes and to the Fabrication of Thin Polysiloxane Coatings.

The branching and cross-linking of siloxane polymers are important processes in silicone technology. A new type of such a process has been developed, which is a self-restructuring of linear polyhydromethylsiloxane (PHMS). This process involves the reorganization of the PHMS to form a highly branched siloxane polymer or finally a cross-linked siloxane network. It occurs through the transfer of a hydride ion between silicon atoms catalyzed by tris(pentafluoromethyl)borane. Its advantage over existing branching and cross-linking reactions is that it runs at room temperature without a low-molecular-weight cross-linker in the absence of water, silanol groups, or other protic compounds and it does not use metal catalysts. The study of this process was carried out in toluene solution. Its course was followed by 1H NMR, 29Si NMR and FTIR, SEC, and gas chromatography. A general mechanism of this new self-restructuring process supported by quantum calculations is proposed. It has been shown that a linear PHMS self-restructured to a highly branched polymer can serve as a pure methylsiloxane film precursor.

Improvement of the chlorine resistance of graphene oxide membranes through siloxane cross-linking

ABSTRACT Nanofiltration membranes exhibit performance deterioration when exposed to highly concentrated chlorinated environments. This is a major challenge of nanofiltration process as chlorine-based chemicals are prevalent within industry for the treatment of organic fouling; thus, making membrane chlorine sensitivity detrimental to sustainable operation. Graphene oxide has an inherent chlorine sensitivity and degrades under exposure to high concentration of chlorine. This work describes a novel nanofiltration membrane fabrication strategy in which Polyethyleneimine and siloxane crosslinking chemistries were used to protect the carboxylic, hydroxyl, and epoxy functional groups of GO nanosheets from the attack of free chlorine. These chemistries were used to improve the chlorine-stability of the GO nanosheets. Polyethyleneimine (PEI) reduces GO and cross-links with oxygenated functional groups preventing their further reaction with chlorine. This chemistry was compared to the chlorine-tolerant siloxane cross-linkers which react with GO’s functional groups to decrease reaction sites. The use of (3-Aminopropyl)triethoxysilane (APTES) and (3-Glycidyloxypropyl)trimethoxysilane (GLYMO) cross-linkers resulted in stable retentions that varied by less than 0.5% following 1,000 ppm chlorine exposure for 1 h. Additionally, GLYMO functionalisation of the GO membrane exhibited exceptional chlorine resistance maintaining a methyl blue retention of 98.0 ± 2.15% following 1 h of exposure 30,000 ppm of chlorine.

Nanogradient Hydrophilic/Hydrophobic Organosilica Membranes Developed by Atmospheric-Pressure Plasma to Enhance Pervaporation Performance.

Organosilica membranes are a promising candidate for pervaporation dehydration owing to their tunable molecular sieving characteristics and excellent hydrothermal stability. Herein, we report a facile modification using an atmospheric-pressure water vapor plasma to enhance the pervaporation performance of organosilica membranes. The surface of methyl-terminated organosilica membranes was treated by water vapor plasma to develop an ultrathin separation active layer suitable for pervaporation dehydration. The surface hydrophilicity was increased by water vapor plasma due to oxidative decomposition of methyl groups to form silanol groups. The plasma-modified layer had a thickness of several nanometers and had a silica-like structure due to the condensation of silanol groups. The plasma-modified organosilica membranes exhibited an improved molecular sieving property owing to the formation of highly cross-linked siloxane networks with a pore size of approximately 0.4 nm. The membranes also exhibited an excellent permselectivity in the dehydration of alcohols due to the nanometer-thick separation active layer with controlled pore size and increased hydrophilicity. The plasma-modified membranes showed high H2O permeance exceeding 10-6 mol m-2 s-1 Pa-1 with permeance ratios for H2O/EtOH and H2O/IPA of 517-3050 and >10 000, respectively, in the dehydration of 90 wt % aqueous solutions at 50 °C, which is among the highest permselectivities for silica-based membranes. Furthermore, the plasma-modified membranes displayed highly efficient dehydration performance for a H2O/MeOH mixture. The H2O permeance and H2O/MeOH permeance ratio in the dehydration of a 90 wt % MeOH aqueous solution at 50 °C were (2.3-3.0) × 10-6 mol m-2 s-1 Pa-1 and 31-143, respectively, which exceeded the permeance-selectivity trade-off of conventional membranes including polymeric, silica-based, and zeolite membranes. The results indicate that the proposed plasma-assisted approach can enhance the pervaporation performance of organosilica membranes via the modification under atmospheric pressure and at room temperature.

Dual-Resistance of Ion Migration and Moisture Erosion via Hydrolytic Crosslinking of Siloxane Functionalized Poly(Ionic Liquids) for Efficient and Stable Perovskite Solar Cells

Dual-Resistance of Ion Migration and Moisture Erosion via Hydrolytic Crosslinking of Siloxane Functionalized Poly(Ionic Liquids) for Efficient and Stable Perovskite Solar Cells

Robust and High-Temperature-Resistant Nanofiber Membrane Separators for Li-Metal, Li-Sulfur, and Aqueous Li-Ion Batteries.

Mechanically strong separators with good electrolyte wettability and low-shrinkage properties are desirable for highly efficient and safe lithium batteries. In this study, multifunctional nanofiber membranes are fabricated by electrospinning a homogeneous solution containing amphiphilic poly(ethylene glycol)diacrylate-grafted siloxane and polyacrylonitrile. After the chemical cross-linking of siloxane, the prepared nanofiber membranes are found to exhibit good mechanical properties, high thermostability, and superior electrolyte-philicity with aqueous and nonaqueous electrolytes. Li-metal cells with the fabricated membrane separator exhibit high cycling stability (Coulombic efficiency of 99.8% after 1000 cycles). Moreover, improved cycling stability of Li-sulfur batteries can be achieved using these membrane separators. These membrane separators can be further used in flexible aqueous lithium-ion batteries and exhibit steady electrochemistry performance. This work opens up a potential route for designing multifunctional universal separators for rechargeable batteries.

Thermally Stable and Solvent-Resistant Conductive Polymer Composites with Cross-Linked Siloxane Network

Doped conjugated polymers can present high electrical conductivity, but their stability against external stimuli such as heat, moisture, and solvent is often limited. Here, we report a design appro...

The Effect of the Type and Concentration of the Crosslinking Diene on the Gas Transport Properties of Membranes Based on Polyoctylmethylsiloxane

The effect of the type and amount of crosslinking reagent on the gas transport properties of polyoctylmethylsiloxane (POMS) membranes is studied for the first time. 1,7-Octadiene (OD), divinyltetramethyldisiloxane (DMDS), and two samples of polydimethylsiloxane (PDMS 500, PDMS 25000 with the molecular weights of 500, 25 000 g/mol, respectively) are used as crosslinking reagents. The permeability, diffusion, and solubility coefficients are measured for n-butane, methane, carbon dioxide, and nitrogen, and the corresponding ideal selectivities of permeability, diffusion, and solubility are calculated. It is shown that the optimal membrane properties of POMS with the use of DMDS as the crosslinking reagent are achieved at a concentration of DMDS of 3%: the maximum values of the permeability coefficient of n-butane (9400 Barrer) and ideal selectivity of permeability of n-butane/methane (26.1). A decrease in both the selectivity of solubility and selectivity of diffusion is observed for the n-butane/methane gas pair in the DMDS, PDMS 500, and PDMS 25000 series of crosslinking reagents with an increase in the fraction of a siloxane crosslinking reagent.

Effect of mercapto-silanes on the functional properties of highly amorphous vinyl alcohol composites with reduced graphene oxide and cellulose nanocrystals

The reinforcing and synergistic effect of a 1D filler (cellulose nanocrystals) and of a 2D filler (reduced graphene oxide) in a high amorphous vinyl alcohol (HAVOH) polymer has been investigated. Nanocomposite films have been obtained by dissolving in water the HAVOH polymer and suitable fillers, thus leading to the formation of a very promising material for eco-friendly food packaging applications. In addition, the effect of (3-Mercaptopropyl) trimethoxysilane as crosslinking agents for the vinylalchol-based polymer has been studied. FTIR and XPS results clearly show that the presence of mercapto silane has a twofold effect. Mercapto groups have the capability to reduce chemically the graphene oxide (GO) filler to reduced graphene oxide (rGO) during the preparation of the HAVOH-based composites and to crosslink the HAVOH structure. Tensile tests show that the effect of siloxane crosslinking leads to an embrittlement of the HAVOH matrix, which is avoided when rGO e cellulose nanocrystals (CNC) are dispersed in the composites. The permeability results show that all the composites exhibit better barrier properties than pristine HAVOH. Particularly, the highest water permeability reduction of about 45% is observed for the sample containing 1% wt/wt GO and 1% wt/wt CNC. This significant drop in permeability is likely related to three concurrent effects, a) the crosslinking of HAVOH matrix, b) the binding of water molecules due to CNC presence and c) the more hydrophobic behaviour associated to a high amount of rGO.

High Thermally Stable and Melt Processable Polyimide Resins Based on Phenylethynyl-Terminated Oligoimides Containing Siloxane Structure.

A series of 4-phenylethnylphthalic anhydride (PEPA)-terminated oligoimides were prepared by co-oligomerizing isomeric dianhydrides, i.e., 2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BPDA), 2,3,3′,4′-benzophenonetetracarboxylic dianhydride (a-BTDA) or 2,3,3′,4′-diphenylethertetracarboxylic dianhydride (a-ODPA), with diamines mixture of bis(4-aminophenoxy)dimethyl silane (APDS) and 2,2′-bis(trifluoromethyl) benzidine (TFDB). The effects of siloxane content and dianhydride structure on the rheological properties of these oligoimides and thermal stability of the corresponding cured polyimide resins were investigated. The results indicated that the introduction of the siloxane structure improved the melt processability of the oligoimides, while the thermal stability of the cured polyimide resins reduced. The oligoimide derived from a-ODPA revealed better melt processability and melt stability due to the existence of a flexible dianhydride structure. The oligoimide PIS-O10 derived from a-ODPA gave the lowest minimum melt viscosity of 0.09 Pa·s at 333 °C and showed the excellent melt stability at 260 °C for 2 h with the melt viscosity in the range of 0.69–1.63 Pa·s. It is also noted that the thermal stability of these resins can be further enhanced by postcuring at 400–450 °C, which is attributed to the almost complete chemical crosslinking of the phenyethynyl combined with oxidative crosslinking of siloxane. The PIS-T10 and PIS-O10 resins that were based on a-BTDA and a-ODPA, respectively, even showed a glass transition temperature over 550 °C after postcuring at 450 °C for 1 h.

Melt fluidity and thermal property of thermosetting siloxane-containing polyimide resins and their organic/inorganic hybrid characteristics

A series of thermosetting siloxane-containing polyimide resins were synthesized by incorporating of bis(p-aminophenoxy)dimethylsilane or bis(p-aminophenoxy)tetramethyldisiloxane with various concentrations into formulated oligoimides. These thermosetting polyimide resins exhibited good combination of processability and thermal resistance. It was found that siloxane-containing oligoimides provided significant advantages over unmodified oligoimides, relative to melt fluidity and processing window, due to the flexibility of D[(CH3)2SiO2/2] siloxy units. The siloxane-containing polyimide resins cured at 380 °C revealed relatively higher glass transition temperatures (Tg) than that of unmodified polyimides, despite the incorporation of flexible siloxane segment in oligoimides. Dynamic mechanical analysis and microstructure investigation suggested that some D[(CH3)2SiO2/2] siloxy units in the surface layer of polyimide transformed into T[CH3SiO3/2] and Q[SiO4/2] siloxy units in the curing procedure besides crosslinking of phenylethynyl groups, due to oxidation crosslinking of siloxane. That led to inorganic silica-like structures formed in situ, and inter-connected by organic polyimide segments. This organic/inorganic hybrid characteristics endowed polyimide resins with enhanced thermal property. After post-curing at 450 °C, D[(CH3)2SiO2/2] siloxy units completely transformed into T[CH3SiO3/2] and Q[SiO4/2] siloxy units, and the polyimide reins gave the Tg even exceeding 550 °C. Meanwhile, the corresponding T700 carbon fiber reinforced composite presented excellent mechanical property and durability at the temperature as high as 500 °C.

SiO2/silicone hybrid superhydrophobic coating on gypsum-based materials with self-cleaning and moisture resistance

Gypsum materials are suffering a shortened service life on account of its poor resistance to moisture and dirt. To overcome such drawbacks, the SiO2/silicone hybrid superhydrophobic surface was introduced on the gypsum surface by the cross-linking of siloxane via sol–gel method. In this study, chemical property and microtopography of the coated surface were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and atomic force microscope (AFM), respectively. Wettability and moisture absorption/desorption tests were carried out to evaluate the superhydrophobicity and moisture resistance of the samples. The results showed that the treated gypsum board had a lower moisture absorption/desorption ratio, compared with the untreated gypsum board (PG). Besides, the coating agent prepared with ethanol and hydrophilic nanosilica particles provided good superhydrophobicity and an optimum moisture-resistance property to the gypsum board. The prepared superhydrophobic surface can endow the material with a self-cleaning effect, protecting it from dust and liquid contamination. The effect mechanism of the solvent and silica particle property on the moisture resistance was discussed in detail. Herein, a green approach is proposed to produce a cleaner gypsum product with extended service life.

In Situ Interface Design in Graphene-Embedded Polymeric Silica Aerogel with Organic/Inorganic Hybridization.

For many practical applications, the most important factor is to have an improved interface between the matrix and dispersed phase in a compressible composite aerogel having a high degree of porosity and a large surface area. Although some measure of compressibility is obtained in polymer-based aerogels with a continuous backbone through the hybridization of the stiff backbone [polyvinyltrimethoxysilane (P-VTMS), -C-C-] and flexible backbone [poly(3-glycidyloxypropyl)trimethoxysilane (P-GPTMS), -C-O-C-], it seems that the extent of improvement is insignificant in terms of interface improvement, surface area increase, and ordered mesoporous network. In this study, the effects of the incorporation of graphene nanoplatelets (GnPs) on aerogels made of a backbone consisting of -C-O-C- (flexible backbone) were examined in terms of structural improvement and were compared with aerogels made of a backbone consisting of -C-C- (stiff backbone). Moreover, the inorganic siloxane cross-link density between the underlying polymer chains was controlled by inducing hydrogen bonding between polymer chains and GnPs. This approach reduces the structural shrinkage during gelation and drying. The integration of only 1 wt % GnP integrated into the backbone by using spinodal decomposition phase separation processing allowed control of the pore size and the surface area. Integration of GnPs through in situ exfoliation during sol-gel transition is shown to be the best approach using the lowest possible amount of GnPs to improve aerogels' mesoporous network made from polymerized GPTMS. A flexible backbone such as P-GPTMS chains is supposed to result in a compliant aerogel, but the chains tend to shrink extensively during gelation and drying, reducing the porosity. P-GPTMS-derived aerogel suffers from a wrong combination of flexible backbone conjugated with an extensive number of permanent chemical cross-links and abundant remaining unreacted hydroxyl groups that undergo permanent chemical shrinkage. To counteract this, the GnP-reinforced prepolymer precursor (P-GPTMS) with fewer siloxane cross-links was synthesized and studied. By use of this strategy, the same elastic properties as those seen with the hybrid P-VTMS- and hybrid P-GPTMS-derived aerogels were imparted, while also improving the mechanical strength by up to 138% and the surface area by up to 205% by controlling the extent of GnP exfoliation during the sol-gel transition. This exceptional effect of GnP on the surface area improvement was shown to be of up to 2.05-fold for P-GPTMS and 2.63-fold for P-VTMS material.

Siloxane crosslinks with dynamic bond exchange enable shape programming in liquid-crystalline elastomers

Liquid crystalline elastomers (LCE) undergo reversible shape changes in response to stimuli, which enables a wide range of smart applications, in soft robotics, adhesive systems or biomedical medical devices. In this study, we introduce a new dynamic covalent chemistry based on siloxane equilibrium exchange into the LCE to enable processing (director alignment, remolding, and welding). Unlike the traditional siloxane based LCE, which were produced by reaction schemes with irreversible bonds (e.g. hydrosilylation), here we use a much more robust reaction (thiol-acrylate/thiol-ene ‘double-click’ chemistry) to obtain highly uniform dynamically crosslinked networks. Combining the siloxane crosslinker with click chemistry produces exchangeable LCE (xLCE) with tunable properties, low glass transition (−30 °C), controllable nematic to isotropic transition (33 to 70 °C), and a very high vitrification temperature (up to 250 °C). Accordingly, this class of dynamically crosslinked xLCE shows unprecedented thermal stability within the working temperature range (−50 to 140 °C), over many thermal actuation cycles without any creep. Finally, multiple xLCE sharing the same siloxane exchangeable bonds can be welded into single continuous structures to allow for composite materials that sequentially and reversibly undergo multiple phase transformations in different sections of the sample.

Antifungal applications for nano-additives synthesized with a bio-based approach

Filamentous fungi are microorganisms that cause deterioration of structural materials due to their ecological plasticity and vegetative functions. Functionalised sol-gel based products can be used to control this kind of biodeterioration through the association to antifungal active additives which are trapped in the siloxane crosslinking. Bioactive additives and materials to control microbial growth have been gaining more attention over the years. However, due to the concern about their toxicity, bio-based approach has been explored. The aim of the present research was to obtain antifungal additives with nanoparticles synthesised with aqueous extract of Senna occidentalis L and silver or copper salts to obtain a functionalised sol-gel based product to control the biodeterioration of bricks. Nanoparticles were characterised by UV–vis spectroscopy, transmission electron microscopy and x-ray diffraction. Silver nanoparticles (15 nm) showed higher stability over time and proved to be active against Aspergillus versicolor and Cladosporium cladosporioides which were isolated from brick wall. The strains were selected due to their high frequency in mycobiota of biodeteriorated structural building materials. The silver nanoparticles were successfully integrated in a silane-based matrix to be applied in bricks. The samples were characterised by surface tension determination, contact angle measurement, water absorption determination, scanning electron microscopy and energy dispersive x-ray spectroscopy. Bricks with the lower concentration (2%) of the functionalised silane (3-mercaptopropyltrimethoxy) showed to be efficient to prevent fungal biofilm development with 100% of inhibition against both strains.