Well-defined side-chain liquid-crystalline polysiloxanes

A route to well-defined side-chain liquid-crystalline polysiloxanes (ratio of weight-to number-average molar masses Mw/Mn < 1.2 is reported. Anionic ring-opening polymerization of pentamethylvinylcyclotrisiloxane yielded a poly(dimethylsiloxane-co-methylvinylsiloxane) backbone. A flexible disiloxane spacer was used to connect 4-(ω-alkenyloxy)-4'-cyanobiphenyl mesogenic molecules to the vinyl groups which belong to the backbone, leading to a side-chain liquid-crystalline polysiloxane (SCLCP) which has its mesogens distributed regularly along the main chain. Preliminary measurements indicate an electro-optic switching time s = 1 min at 20°C and 7 s at 32°C (dc, 5 V/µm))

Pattern transfer fidelity in capillary force lithography with poly(ferrocenylsilane) plasma etch resists

The influence of processing conditions and polymer architecture on pattern transfer in capillary force lithography (CFL) using poly(ferrocenylsilane) etch resists is investigated. Zero-shear-rate viscosities measured at different temperatures and for polymers with different molar masses are related to the quality of CFL patterns, assessed based on atomic force microscopy experiments. An optimal range of viscosities corresponding to appropriate molar masses and processing temperatures is established. In this range, polymers possess enough mobility allowing for reasonably quick surface pattern formation. Yet, the polymers are not too mobile and preserve their shape when quenched to below Tg prior to serving as etch resist masks

Smart Windows: Switching Light Transmittance by Responsive Organometallic Poly(ionic liquid)s: Control by Cross Talk of Thermal and Redox Stimuli (Adv. Funct. Mater. 41/2017)

In article number 1702784, G. Julius Vancso and co-workers report an organometallic polymer with sulfonate side groups for transmittance control. The novel polymer, produced by a simple one-step synthesis, exhibits both a lower critical solution temperature (LCST)-type phase transition and an “isothermal” redox-triggered phase transition in aqueous solution, leading to a new type of “smart window” by using thermal and electrical triggers

Dual functionality of ferrocene-based metallopolymers as radical scavengers and nanoparticle stabilizing agents

The beneficial redox properties of ferrocene-based polymers have been utilized during in situ preparation of metallic nanoparticles, while such redox features also indicate great promise in applications as free radical..

Collapse from the top: Brushes of poly(N-isopropylacrylamide) in co-nonsolvent mixtures

Using a combination of ellipsometry and friction force microscopy, we study the reversible swelling, collapse and variation in friction properties of covalently bound poly(N-isopropylacrylamide) (PNIPAM) layers on silicon with different grafting densities in response to exposure to good solvents and cononsolvent mixtures. Changes in the thickness and segment density distribution of grafted films are investigated by in situ ellipsometry. Based on quantitative modelling of the ellipsometry spectra, we postulate a structural model, which assumes that collapse takes place in the contacting layer between the brush and the co-nonsolvent and the top-collapsed brushes remain hydrated in the film interior. Using the structural model derived from ellipsometry spectra, we analyse the AFM based friction force microscopy data, which were obtained by silica colloidal probes. Results show a large increase of the friction coefficient of PNIPAM grafts when the grafts swollen by water are brought in contact with cononsolvents. For instance, the value of the friction coefficient for a medium density brush in water is four times lower than the value observed in a water–methanol (50% v/v) mixture. This increase of friction is accompanied by an increase in adherence between the PNIPAM chains and the silica colloidal probes, and is a result of chain collapse in the graft when contacted by a co-nonsolvent mixture in agreement with the model postulated on the basis of ellipsometric characterisation. The kinetic behaviour of the collapse is assessed by measuring the temporal variation of friction in situ as a function of elapsed time following contact with the co-nonsolvent as a function of graft density. In conclusion, the effect of cononsolvency influenced both the thickness of the PNIPAM brushes and the tribological behavior of the brush surfaces

Comparing amine- and ammonium functionalized silsesquioxanes for large scale synthesis of hybrid polyimide high-temperature gas separation membranes

PolyPOSS-imide membranes are promising for separating H2 from larger molecules (CO2, N2, CH4) at temperatures up to 300 °C. Their fabrication involves two steps: interfacial polymerization of POSS and 6FDA, followed by thermal imidization. This work provides a systematic study of the effects of cations on membrane properties and performance. For this, two distinct POSS molecules were used: functionalized with -NH3+Cl− or, so far unexplored, -NH2. The ammonium groups are partially deprotonated by using three different bases, LiOH, NaOH, and KOH. We demonstrate that the introduced cations affect the film thickness but not the molecular composition of the polyamic acid. All polyamic acids can be imidized, but the cations reduce the imidization kinetics as well as the loss of organic crosslinkers. For flat disc membranes, at 200 °C, the absence of cations results in comparable permeability combined with higher selectivity for H2/N2. This, and the possibility to discard adding a base, motivated a scale-up study of the new POSS. For tubular membranes, much higher ideal and mixed gas selectivities are found than for membranes where NaOH was added. Results indicate that the new route allows more reproducible production of defect free membranes and has potential for larger-scale polyPOSSimide fabrication.publishedVersio

Poly(ferrocenylsilanes) as Etch Barriers in Nano and Microlithographic Applications

Thin films of organic-organometallic block copolymers are shown to be efficient self-assembled templates for nanolithography. Block copolymers composed of organic blocks such as polyisoprene or polystyrene and a poly(ferrocenylsilane) block microphase separate to form a monolayer of densely packed organometallic spheres in an organic matrix. The high resistance of the organometallic phase to reactive ion etching enables the nanoscale patterns to be transferred into silicon substrates, forming nano structured surfaces. Electrostatic self-assembly of poly(ferrocenylsilane) polyanions and polycations is discussed as a means to form laterally structured organometallic multilayer thin films by area-selective adsorption onto chemically patterned substrates

Dual functionality of ferrocene-based metallopolymers as radical scavengers and nanoparticle stabilizing agents

The beneficial redox properties of ferrocene-based polymers have been utilized during in situ preparation of metallic nanoparticles, while such redox features also indicate great promise in applications as free radical scavengers. Here, colloidal dispersions of an antioxidant nanozyme composed of amidine-functionalized polystyrene latex nanoparticles (AL), negatively charged poly(ferrocenylsilane) (PFS(-)) organometallic polyions, and ascorbic acid (AA) were formulated. AL was first functionalized with PFS(-). Increasing the polymer dose resulted in charge neutralization and subsequent charge reversal of the particles. The strength of repulsive interparticle forces of electrostatic origin was significant at low and high doses leading to stable colloids, while attractive forces dominated near the charge neutralization point giving rise to unstable dispersions. The saturated PFS(-) layer adsorbed on the surface of AL (p-AL nanozyme) enhanced the colloidal stability against salt-induced aggregation without affecting the pH-dependent charge and size of the particles. The joint effect of PFS(-) and AA in radical decomposition was observed indicating the antioxidant potential of the system. The immobilization of PFS(-) deteriorated its scavenging activity, yet the combination with AA improved this feature. The results indicate that p-AL-AA is a promising radical scavenger since the high colloidal stability of the particles allows application in heterogeneous systems, such as in industrial manufacturing processes, where antioxidants are required to maintain acceptable product quality

An adapted mindfulness intervention for people with dementia in care homes: feasibility pilot study

OBJECTIVE: Depression and anxiety are common in dementia. There is a need to develop effective psychosocial interventions. This study sought to develop a group-based adapted mindfulness programme for people with mild to moderate dementia in care homes and to determine its feasibility and potential benefits. METHODS: A manual for a 10-session intervention was developed. Participants were randomly allocated to the intervention plus treatment as usual (n = 20) or treatment as usual (n = 11). Measures of mood, anxiety, quality of life, cognitive function, stress and mindfulness were administered at baseline and 1 week post-intervention. RESULTS: There was a significant improvement in quality of life in the intervention group compared to controls (p = 0.05). There were no significant changes in other outcomes. CONCLUSIONS: The intervention was feasible in terms of recruitment, retention, attrition and acceptability and was associated with significant positive changes in quality of life. A fully powered randomised controlled trial is required. Copyright © 2017 John Wiley & Sons, Ltd