Critical behavior of confined supramolecular soft materials on a microscopic scale

The formation of fiber networks and the resulting rheological properties of supramolecular soft materials are dramatically influenced when the volume of the system is reduced to a threshold. Unlike un-confined systems, the formation of fiber networks under volume confinement is independent of temperature and solute concentration.

Force amplification response of actin filaments under confined compression

Actin protein is a major component of the cell cytoskeleton, and its ability to respond to external forces and generate propulsive forces through the polymerization of filaments is central to many cellular processes. The mechanisms governing actin's abilities are still not fully understood because of the difficulty in observing these processes at a molecular level. Here, we describe a technique for studying actin–surface interactions by using a surface forces apparatus that is able to directly visualize and quantify the collective forces generated when layers of noninterconnected, end-tethered actin filaments are confined between 2 (mica) surfaces. We also identify a force-response mechanism in which filaments not only stiffen under compression, which increases the bending modulus, but more importantly generates opposing forces that are larger than the compressive force. This elastic stiffening mechanism appears to require the presence of confining surfaces, enabling actin filaments to both sense and respond to compressive forces without additional mediating proteins, providing insight into the potential role compressive forces play in many actin and other motor protein-based phenomena.

Dynamics of force generation by confined actin filaments

Forces generated by polymerizing/de-polymerizing actin filaments confined between two mica surfaces were measured using the Surface Forces Apparatus. The measurements show that confined actin filaments exhibit complex force-generation dynamics involving multiple “modes”, the predominance of which is determined by the confinement gap and the applied force (confining pressure).

Distinct kinetics of molecular gelation in a confined space and its relation to the structure and property of thin gel films

Thin films of molecular gels formed in a confined space have potential applications in transdermal delivery, artificial skin, molecular electronics, etc. The microstructures and properties of thin gel films can be significantly different from those of their bulk counterparts. However, so far a comprehensive understanding of the effects of spatial confinement on the molecular gelation kinetics, fiber network structure and related mechanical properties is still lacking. In this work, using rheological techniques, we investigated the effect of one-dimensional confinement on the formation kinetics of fiber networks in the molecular gelation process. Fractal analyses of the kinetic information in terms of an extended Dickinson model enabled us to describe quantitatively the distinct kinetic signature of molecular gelation. The structural features derived from gelation kinetics support well the fractal patterns of the fiber networks acquired by optical and electron microscopy. With the kinetics-structure correlation, we can gain an in-depth understanding of the confinement-induced differences in the structure and consequently the mechanical properties of a model molecular gelling system. Particularly, the confinement induced structural transition, from a three-dimensional, dense and compact spherulitic network composed of highly branched fibers to a quasi-two-dimensional sparse spherulitic network composed of less branched fibers and entangled fibrils at the boundary areas, renders a gel film to become less stiff but more ductile. Our study suggests here a new strategy of engineering the fiber network microstructure to achieve functional gel films with unusual but useful properties.

Experimental study of damage evolution in cuboid stirrup-confined concrete

This paper presents an experimental study on cuboid stirrup-confined concrete specimens under uniaxial monotonic loading and cyclic loading. The effects of stirrup volume ratio, stirrup yield strength, and concrete strength on damage evolution of the stirrup-confined concrete were investigated. The experimental results showed that the strength and ductility of concrete are improved by appropriate arrangement of the stirrup confinement. Firstly, with the increase of the stirrup volume ratio, the damage evolution of concrete can be relatively restrained. Secondly, higher stirrup yield strength usually leads to larger confining pressures and slower damage evolution. In contrast, higher concrete strength leads to higher brittleness, which accelerates damage evolution. Based on the experimental data, a plastic strain expression is obtained through curve fitting, and a damage evolution equation for stirrup-confined concrete is proposed by introducing a confinement factor (C). The comparisons results demonstrated that the proposed damage evolution curve can accurately describe the experimental results.

Evaluation of the mechanical performance of short concrete column confined with CFRP and GFRP

Concrete has been successfully used to build strong and economic structures. However severe environmental exposures slowly deteriorate concrete strength until complete failure reducing its designed service life. Fiber Reinforced Polymer “FRP” has been recently introduced in the construction industry to strengthen and retrofitting several structural elements including columns. In this research two types of FRP have been used to wrap concrete column in order to increase its capacity; these are Carbon Fiber Reinforced Polymer “CFRP” and Glass Fiber Reinforced Polymer “GFRP”. Twelve short concrete columns have been wrapped with one and two FRP layers including CFRP and GFRP to evaluate their mechanical performance. Mechanical testing has shown that, in general, concrete columns wrapped with FRP produced higher modulus of elasticity compared to the control sample. Results showed that one layer of CFRP have 85.8% increases where as one layer of GFRP showed an increase of 64.5%. Furthermore, two layers of CFRP and GFRP showed 112.5% and 77.2% increase respectively.

Strength reduction in square columns confined with CFRP under marine environment

The performance of carbon fibre reinforced polymer (CFRP) wrapped square column under the wet/dry cycle of marine environment is studied in this paper. Two different types of epoxies (one commercial and one modified) are used to bond CFRP with concrete to investigate their suitability under the harsh environmental exposure. The experimental results are verified against the available theoretical models of square column and a reduction factor is derived to incorporate the effect of marine exposure to estimate the strength reduction for the columns in general. The accuracy of the proposed reduction factor is then verified by predicting the degraded strength of the columns which are currently available in the literature.

Electrostatically confined plasma in segmented hollow cathode geometries for surface engineering

A segmented hollow cathode (SHC) geometry was used for electrostatic confinement of plasma, and surface engineering treatments were conducted in this arrangement. The assessed processes included plasma nitriding, reactive deposition of sputtered material, and deposition of carbonaceous films by plasma-enhanced chemical vapor deposition with a bipolar pulsed-dc power supply on steel substrates. The treated specimens exhibited uniform surface morphology and deposition layers. Characterization techniques included optical microscopy, scanning electron microscopy with energy dispersive X-ray capability, and X-ray diffraction. The advantages and potential applications of the SHC arrangement are discussed in view of these results.