High-Strength Liquid Crystal Polymer-Graphene Oxide Nanocomposites from Water.

We report on the morphology and mechanical properties of nanocomposite films derived from aqueous, hybrid liquid crystalline mixtures of rodlike aggregates of a sulfonated, all-aromatic polyamide, poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT), and graphene oxide (GO) platelets. An isothermal step at 200 °C facilitates in situ partial thermal reduction of GO to reduced GO (rGO) in nanocomposite films. X-ray scattering studies reveal that PBDT-rGO nanocomposites exhibit both higher in-plane alignment of PBDT (the order parameter increases from 0.79 to 0.9 at 1.8 vol % rGO) and alignment along the casting direction (from 0.1 to 0.6 at 1.8 vol % rGO). From dynamic mechanical thermal analysis, the interaction between PBDT and rGO causes the ß-relaxation activation energy for PBDT to increase with rGO concentration. Modulus mapping of nanocomposites using atomic force microscopy demonstrates enhanced local stiffness, indicating reinforcement. From stress-strain analysis, the average Young's modulus increases from 16 to 37 GPa at 1.8 vol % rGO and the average tensile strength increases from 210 to 640 MPa. Despite polymer alignment along the casting direction, an average transverse tensile strength of 230 MPa is obtained.

A mucoadhesive biodissolvable thin film for localized and rapid delivery of lidocaine for the treatment of vestibulodynia.

Vestibulodynia (VBD), an idiopathic pain disorder characterized by erythema and pain of the vulvar vestibule (the inner aspect of the labia minora and vaginal opening), is the most common cause of sexual pain for women of reproductive age. Women also feel discomfort with contact with clothing and tampon use. As most women with this disorder only have pain with provocation of the tissue, topical anesthetics applied to the vestibule are the current first line treatment for temporary pain relief. Treatment options are limited due to anatomical constraints of the vestibular region, poor drug retention time, imprecise dosing, leakage, and overall product messiness. In this study we report a novel approach to treatment of VBD using thin film designed to fit the vulvar vestibule and deliver lidocaine locally. Two use cases for VBD treatment were identified 1) rapid drug release (<5 min), for use prior to intercourse and 2) long-acting release (≥120 min) for prolonged use and relief throughout the day. Cellulose-based mucoadhesive thin films were fabricated using a solvent casting method. Three polymers including hydroxyethylcellulose (HEC), hydroxypropylcellulose (HPC), and hydroxypropylmethycellulose (HMPC), were selected owing to their biocompatibility and ideal properties for film casting. Films casted with HEC, HPC, and HPMC exhibited mucoadhesive properties relative to a control, with the highest mucoadhesive force recorded for films casted with HPC. Effect of media volume, pH, presence of mucin and presence of drug on film dissolution rates were investigated. Dissolution rates were independent of media volume, media pH or drug presence, whereas faster dissolution rates were obtained for all films in presence of mucin. In vitro lidocaine release kinetics were influenced by polymer type, percent drug loading and film casting thickness. Lidocaine release was based on a diffusion mechanism rather than through film dissolution and faster release (∼5 min) was observed for HEC films compared HPC films (∼120 min). Higher drug loading and film thickness resulted in slower and more prolonged release kinetics of lidocaine. All films were biocompatible and exhibited good mechanical properties. Two film formulations (9% w/w HPC with 12% w/w LHC, 5% w/w HEC with 6% w/w LHC) were optimized to meet the two use case scenarios for VBD treatment and moved into in vivo testing. In vivo testing demonstrated the safety of the films in BALB/c mice, and the pharmacokinetic analysis demonstrated the delivery of lidocaine primarily to the vaginal tissue. We demonstrate the ability to develop a mucoadhesive, biodissolvable thin film and fine-tune drug release kinetics to optimize local delivery of lidocaine to the vulva.

Observation of transition cascades in sheared liquid crystalline polymers.

We report on the shear rheology of liquid crystalline solutions composed of charged, rodlike polymers that form supramolecular assemblies dispersed in water. Under steady shear, we observe shear thickening behavior, followed by a hesitation in the viscosity accompanied by an extremely narrow range of negative first normal stress difference. The Peclet number (Pe, shear rate normalized by rod rotational diffusivity) for the onset of shear thickening is in agreement with previous, high-resolution numerical simulations of the Doi-Edwards-Hess kinetic theory. We interrogate these dynamic responses through shear step-down experiments, revealing a complex evolution of transient responses. Detailed analysis of the stress transients provides compelling evidence that the principal axis of the rod orientational distribution, the nematic director, undergoes a cascade of transitions and coexistence of periodic states known as kayaking, tumbling, and wagging, before transitioning to steady flow alignment above a critical shear rate.

Strong graphene oxide nanocomposites from aqueous hybrid liquid crystals.

Combining polymers with small amounts of stiff carbon-based nanofillers such as graphene or graphene oxide is expected to yield low-density nanocomposites with exceptional mechanical properties. However, such nanocomposites have remained elusive because of incompatibilities between fillers and polymers that are further compounded by processing difficulties. Here we report a water-based process to obtain highly reinforced nanocomposite films by simple mixing of two liquid crystalline solutions: a colloidal nematic phase comprised of graphene oxide platelets and a nematic phase formed by a rod-like high-performance aramid. Upon drying the resulting hybrid biaxial nematic phase, we obtain robust, structural nanocomposites reinforced with graphene oxide.

Irreversible Shear-Activated Gelation of a Liquid Crystalline Polyelectrolyte.

We report irreversible, shear-activated gelation in liquid crystalline solutions of a rigid polyelectrolyte that forms rodlike assemblies (rods) in salt-free solution. At rest, the liquid crystalline solutions are kinetically stable against gelation and exhibit low viscosities. Under steady shear at, or above, a critical shear rate, a physically cross-linked, nematic gel network forms due to linear growth and branching of the rods. Above a critical shear rate, the time scale of gelation can be tuned from hours to nearly instantaneously by varying the shear rate and solution concentration. The shear-activated gels are distinct in their structure and rheological properties from thermoreversible gels. At a fixed concentration, the induction time prior to gelation decreases exponentially with the shear rate. This result indicates that shear-activated thermalization of the electrostatically stabilized rods overcomes the energy barrier for rod-rod contact, enabling rod fusion and subsequent irreversible network formation.

Nanofibrillar Ionic Polymer Composites Enable High-Modulus Ion-Conducting Membranes.

Polymer electrolyte membranes (PEMs) with high volume fractions of ionic liquids (IL) and high modulus show promise for enabling next-generation gas separations, and electrochemical energy storage and conversion applications. Herein, we present a conductive polymer-IL composite based on a sulfonated all-aromatic polyamide (sulfo-aramid, PBDT) and a model IL, which we term a PBDT-IL composite. The polymer forms glassy and high-aspect-ratio hierarchical nanofibrils, which enable fabrication of PEMs with both high volume fractions of IL and high elastic modulus. We report direct evidence for nanofibrillar networks that serve as matrices for dispersed ILs using atomic force microscopy and small- and wide-angle X-ray scattering. These supramolecular nanofibrils form through myriad noncovalent interactions to produce a physically cross-linked glassy network, which boasts the best combination of room-temperature modulus (0.1-2 GPa) and ionic conductivity (8-4 mS cm-1) of any polymer-IL electrolyte reported to date. The ultrahigh thermomechanical properties of our PBDT-IL composites provide high moduli (∼1 GPa) at temperatures up to 200 °C, enabling a wide device operation window with stable mechanical properties. Together, the high-performance nature of sulfo-aramids in concert with the inherent properties of ILs imparts PBDT-IL composites with nonflammability and thermal stability up to 350 °C. Thus, nanofibrillar ionic networks based on sulfo-aramids and ILs represent a new design paradigm affording PEMs with exceptionally high moduli at exceedingly low polymer concentrations. This new design strategy will drive the development of new high-performance conductive membranes that can be used for the design of gas separation membranes and in electrochemical applications, such as fuel cells and Li-metal batteries.