Reversible friction regulation is of long-standing great interest in the fields of both industry and scientific research, so some materials and theories have been developed aiming to solve this problem. Light-sensitive materials are promising because of the easy controllable switching of the properties and structures. Here, a reversible light-controlled macrolubrication was realized by regulating the performance of nanoscale light-sensitive molecules adsorbed on contact surfaces. In this work, symmetric diarylethene and asymmetric diarylethene had been designed and synthesized as functional materials. The friction forces were found to be obviously increased upon exposure to ultraviolet light and decayed to the initial value under visible light. In addition, the friction coefficient changed alternately with ultraviolet and visible illumination. According to the results of experiments and simulation of material properties, the behavior was suggested to be attributed to the difference in shear stiffness of the nanoscale diarylethene molecule adsorption layer triggered by two wavelength lights. This work not only provides a new lubrication regulation technology but also develops intelligent engineering materials.

Block copolymers composed of hard and soft segments form an interesting class of materials ranging from thermoplastics to thermoplastic elastomers depending on their composition and/or the size of segments. These materials have attracted much attention in the past decade because by careful tailoring, polymers of desired properties can be obtained. Yet they are thermoplastic in nature and can be processed and even reprocessed thermally. Among the common elastomers that can be used as the soft segment in a block copolymer, polydimethyl-siloxane is of special interest due to its great thermal stability at elevated temperatures and high flexibility at low temperatures. Block copolymers containing polydimethylsiloxane as the soft segment and various thermoplastics such as poly(α-methylstyrene), polystyrene, and polysulfone, etc., as the hard segment, have been synthesized and studied. A group of randomly alternating block copolymers of bisphenol-A polycarbonate and polydimethylsiloxane have also been prepared by in situ polymerization of dichloro-terminated siloxane oligomers and bisphenol-A and phosgene. The properties of these block copolymers as well as those of the others have been discussed to some extent in a general review. This work reports the results of a study on the structure-property relationship of a series of perfectly alternating block copolymers of bisphenol-A polycarbonate and polydimethylsiloxane synthesized via different routes. They were prepared by silylamine-hydroxyl reaction. Slightly less than the stoichiometric quantity of siloxane oligomers was incrementally added to a hydrated solution of the polycarbonate in refluxing chlorobenzene. The reaction can be represented by the simple scheme:

Fluid viscosity is ubiquitous property and is of practical importance in intelligent fluids, industrial lubrication, and pipeline fluid transportation. Recently, there has been a surging interest in viscosity regulation. Here, we have developed a group of photorheological fluids by utilizing azobenzene polymers with a light-induced microstructure transformation. In this work, a photosensitive polymer with 4,4′-bis-hydroxyazobenzene as the main chain was designed and synthesized as a pivotal functional material. The sufficiently large structural difference under ultraviolet and near-infrared light makes it possible to regulate the viscosity of a polyethylene glycol solution. The viscosity of the photosensitive rheological fluids under ultraviolet light radiation is found to be up to 45.1% higher than that under near-infrared light radiation. To explore this intelligent lubricating technology, the friction regulation of ceramic sliding bearings was investigated utilizing photosensitive rheological fluids. Reversible friction regulation with a ratio of up to 3.77 has been achieved by the alternative irradiation of near-infrared and ultraviolet light, which can be attributed to the differences in mechanical properties and molecular structures under ultraviolet and near-infrared light according to both simulations and experiments. Such photorheological fluids will have promising applications in controllable lubrication, intelligent rheological fluids, and photosensitive dampers.

The relationships between the properties and microstructures of two series of perfectly alternating bisphenol A-polycarbonate-polydimethylsiloxane block copolymers were studied. In the first series, the polycarbonate (PC) block length was kept constant while the block length of polydimethylsiloxane (PDMS) was varied. The tensile properties of these block copolymers were found to be a function of composition. Dynamic mechanical properties measured as a function of temperature revealed the two-phase nature of these materials. Transmission electron micrographs showed that all samples had a sponge-like morphology independent of composition. The rheological maximum viscosity for the sample containing PC and PDMS blocks of equal molecular weight and extrudate swells increased with PC content. Takayamagi's mechanical coupling model was used to predict the maximum loss tangent at the glass transition temperature of PDMS using the known properties of pure components. The predictions agreed fairly well with the experimental results. In a second series of block copolymers, the block molecular weights of both PC and PDMS were varied to keep the composition constant. The tensile strength of these samples was found to increase with block molecular weights, except for the sample having the highest block molecular weights. The lower tensile strength of this material was attributed to its lamellar type morphology. Cold crystallization of PDMS blocks was found for samples having high PDMS block molecular weight (greater than 8000 g/mole). The Tg of PC blocks followed the Fox-Flory equation with a higher K value than expected. The PDMS content in PC domains was calculated to range from 11% for material of low block molecular weights to about 1.3% for high block molecular weight material.

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