Graphene as a photothermal actuator for control of lipid mesophase structure

Photothermal Nanomaterials: A Powerful Light-to-Heat Converter

All forms of energy follow the law of conservation of energy, by which they can be neither created nor destroyed. Light-to-heat conversion as a traditional yet constantly evolving means of converting light into thermal energy has been of enduring appeal to researchers and the public. With the continuous development of advanced nanotechnologies, a variety of photothermal nanomaterials have been endowed with excellent light harvesting and photothermal conversion capabilities for exploring fascinating and prospective applications. Herein we review the latest progresses on photothermal nanomaterials, with a focus on their underlying mechanisms as powerful light-to-heat converters. We present an extensive catalogue of nanostructured photothermal materials, including metallic/semiconductor structures, carbon materials, organic polymers, and two-dimensional materials. The proper material selection and rational structural design for improving the photothermal performance are then discussed. We also provide a representative overview of the latest techniques for probing photothermally generated heat at the nanoscale. We finally review the recent significant developments of photothermal applications and give a brief outlook on the current challenges and future directions of photothermal nanomaterials.

Liquid phase IR detector based on the photothermal effect of reduced graphene oxide-doped liquid crystals

Owing to the additional functionalities endowed by nanoparticle dopants, liquid crystals doped with nanoparticles are promising optical materials in a wide range of applications. In this study, we exploited the photothermal effect of reduced graphene oxide (rGO)-doped 5CB nematic liquid crystals (LC-rGO) to develop an infrared (IR) detector that is not only sensitive to IR but also measures the temperature and energy deposited in the detector. We demonstrate that rGO doping in LCs significantly enhances the IR absorption and transforms the light energy into thermal energy through the photothermal effect. The changes in the orientational order and birefringence of the LC-rGO induced by the photothermal effect under IR irradiation were manifested as an instantaneous color change in the white light probe beam. The change in the probe beam intensity was further translated into a temperature change and energy deposited in the detector. We also demonstrated that the external voltage applied to the detector significantly amplifies the photothermal responsivity by compensating for the anchoring energy of the LC. This study proposes a novel technology for detecting IR, temperature, and energy deposited in the detector by means of visible light, which has significant potential for developing large-area and high-resolution IR detectors by exploiting mature liquid crystal display technologies.

Hexaarylbiimidazoles(HABI)-functionalized lyotropic liquid crystalline systems as visible light-responsive materials

Hexaarylbiimidazoles (HABIs) are a promising class of photoswitchable molecule that have received little attention in the literature. Among them, (2,2'-dimethoxydiphenylimidazole)-1,1'-binaphthyl (HABI1) displays unusual negative photochromism and is responsive to green light. This study investigates the potential of HABIs to serve as photo-responsive actuators controlling the structure of lyotropic liquid crystalline (LLC) materials. HABI1 with four methyl chains and HABI2 with four dodecyl chains were synthesized. Time resolved small angle X-ray scattering was used to characterize the potential disruptive effects of HABIs on the nanostructure of LLC systems. HABIs underwent rapid isomerization under irradiation, with a very slow reversion in the dark in toluene and in the LLC matrix, demonstrating excellent stability and photo-fatigue resistant. HABIs completely triggered phase transitions in the phytantriol-based materials, and HABI2 generated a greater disruption than HABI1 on the lipid packing due to the enhanced steric influence. Tuning the lipid composition yielded systems that transitioned from a "slow release" lamellar phase to a "burst release" bicontinuous cubic phase upon light irradiation. Such systems therefore may exhibit a triggered release behavior upon a short time of irradiation, showing great potential in "on demand" drug delivery.

Characterization of Lipid-Based Lyotropic Liquid Crystal and Effects of Guest Molecules on Its Microstructure: a Systematic Review

Liquid crystals (LCs) are conventionally divided into thermotropic or lyotropic, based on the organization and sequence of the controlled molecular system. Lipid-based lyotropic liquid crystal (LLC), such as lamellar (Lα), bicontinuous cubic (Q_II), or hexagonal (H_II) phases, have attracted wide interest in the last few decades due to their practical potential in diverse applications and notable structural complexity. Various guest molecules, such as biopharmaceuticals, chemicals, and additives, can be solubilized in either aqueous or oily phase. And the LLC microstructure can be altered to affect the rate of drug release eventually. To utilize these microstructural variations to adjust the drug release in drug delivery system (DDS), it is crucial to understand the structure variations of the LLC caused by different types of guest molecules. Therefore, in this article, we review the effect of guest molecules on lipid-based LLC microstructures. In particular, we focus on the different characterization methods to evaluate this change caused by guest substances, such as polarized light microscopy (PLM), small-angle X-ray scattering (SAXS), Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), self-diffusion nuclear magnetic resonance (SD-NMR), and so on.