Production of Organizational Chiral Structures by Design.

Organizational chirality on surfaces has been of interest in chemistry and materials science due to its scientific importance as well as its potential applications. Current methods for producing organizational chiral structures on surfaces are primarily based upon the self-assembly of molecules. While powerful, the chiral structures are restricted to those dictated by surface reaction thermodynamics. This work introduces a method to create organizational chirality by design with nanometer precision. Using atomic force microscopy-based nanolithography, in conjunction with chosen surface chemistry, various chiral structures are produced with nanometer precision, from simple spirals and arrays of nanofeatures to complex and hierarchical chiral structures. The size, geometry, and organizational chirality is achieved in deterministic fashion, with high fidelity to the designs. The concept and methodology reported here provide researchers a new and generic means to carry out organizational chiral chemistry, with the intrinsic advantages of chiral structures by design. The results open new and promising applications including enantioselective catalysis, separation, and crystallization, as well as optical devices requiring specific polarized radiation and fabrication and recognition of chiral nanomaterials.

Light-triggered thermal conductivity switching in azobenzene polymers.

Materials that can be switched between low and high thermal conductivity states would advance the control and conversion of thermal energy. Employing in situ time-domain thermoreflectance (TDTR) and in situ synchrotron X-ray scattering, we report a reversible, light-responsive azobenzene polymer that switches between high (0.35 W m-1 K-1) and low thermal conductivity (0.10 W m-1 K-1) states. This threefold change in the thermal conductivity is achieved by modulation of chain alignment resulted from the conformational transition between planar (trans) and nonplanar (cis) azobenzene groups under UV and green light illumination. This conformational transition leads to changes in the π-π stacking geometry and drives the crystal-to-liquid transition, which is fully reversible and occurs on a time scale of tens of seconds at room temperature. This result demonstrates an effective control of the thermophysical properties of polymers by modulating interchain π-π networks by light.

Spatially Selective and Density-Controlled Activation of Interfacial Mechanophores.

Mechanically sensitive molecules known as mechanophores have recently attracted much interest due to the need for mechanoresponsive materials. Maleimide-anthracene mechanophores located at the interface between poly(glycidyl methacrylate) (PGMA) polymer brushes and Si wafer surfaces were activated locally using atomic force microscopy (AFM) probes to deliver mechanical stimulation. Each individual maleimide-anthracene mechanophore exhibits binary behavior: undergoing a retro-[4 + 2] cycloaddition reaction under high load to form a surface-bound anthracene moiety and free PGMA or remaining unchanged if the load falls below the activation threshold. In the context of nanolithography, this behavior allows the high spatial selectivity required for the design and production of complex and hierarchical patterns with nanometer precision. The high spatial precision and control reported in this work brings us closer to molecular level programming of surface chemistry, with promising applications such as 3D nanoprinting, production of coatings, and composite materials that require nanopatterning or texture control as well as nanodevices and sensors for measuring mechanical stress and damage in situ.

Microfluidics Synthesis of Gene Silencing Cubosomes.

The success of gene technologies hinges on our ability to engineer superior encapsulation and delivery vectors. Cubosomes are lipid-based nanoparticles where membranes, instead of enveloping into classic liposomes, intertwine into complex arrays of pores well-ordered in a cubic lattice. These complex nanoparticles encapsulate large contents of siRNA compared to a liposomal analogue. Importantly, the membranes that form cubosomes have intrinsic fusogenic properties that promote fast endosomal escape. Despite the great potential, traditional routes of forming cubosomes lead to particle sizes too large to fulfill the state-of-the art requirements of delivery vectors. To overcome this challenge, we utilize a microfluidic nanomanufacturing device to synthesize cubosomes and siRNA-loaded cubosomes, termed cuboplexes. Utilizing cryogenic TEM and small angle X-ray scattering we elucidate the time-resolved mechanisms in which microfluidic devices allow the production of small cubosomes and cuboplexes (75 nm) that outperform commercially available delivery vectors, as well as liposome-based systems.

Interfacial Mechanophore Activation Using Laser-Induced Stress Waves.

A new methodology is developed to activate and characterize mechanochemical transformations at a solid interface. Maleimide-anthracene mechanophores covalently anchored at a fused silica-polymer interface are activated using laser-induced stress waves. Spallation-induced mechanophore activation is observed above a threshold activation stress of 149 MPa. The retro [4+2] cycloaddition reaction is confirmed by fluorescence microscopy, XPS, and ToF-SIMS measurements. Control experiments with specimens in which the mechanophore is not covalently attached to the polymer layer exhibit no activation. In contrast to activation in solution or bulk polymers, whereby a proportional increase in mechanophore activity is observed with applied stress, interfacial activation occurs collectively with spallation of the polymer film.