Mechanisms of Hydrophobic Recovery of Poly(dimethylsiloxane) Elastomers after Plasma/Corona Treatments: A Minireview.

Plasma/corona treatment could alter the wettability of a poly(dimethylsiloxane) (PDMS) surface from being hydrophobic to being hydrophilic, which has attracted many researchers' attention. However, the treated surface will gradually recover its hydrophobicity as it ages. To understand the recovery, many studies have been performed.

Dynamics of microbial-induced oil degradation at the microscale.

Microbial-induced oil degradation (MIOD) has a wide range of applications, such as microbial enhanced oil recovery and bioremediation of oil pollution. However, our understanding of MIOD is still far from complete. Particularly, how is the dynamics of degradation process at the microscale level with a single-cell resolution remains to be disclosed.

Oscillation of type IV pili regulated by the circadian clock in cyanobacterium PCC7942.

Type IV pili (TFP) are known to be functionally related to cell motilities and natural transformation in many bacteria. However, the molecular and ecological functions of the TFP have rarely been reported for photosynthetic cyanobacteria. Here, by labeling pili in model cyanobacterium PCC 7942 (Syn7942), we have quantitatively characterized the TFP and its driven twitching motility in situ at the single-cell level.

Factors Influencing Initial Adhesion and Evolution at the Dodecane-Water Interface.

Bacterial adhesion and evolution at the oil-water interface are important for a broad range of applications such as food manufacturing and microbial-enhanced oil recovery, etc. However, our understanding on bacterial interfacial adhesion and evolution, particularly at the single-cell level, is still far from complete. In this work, by employing PAO1 at the dodecane-water interface as a model system, we have studied the effects of different factors on bacterial interfacial adhesion and the dynamic evolution of bacterial interfacial behavior at the single-cell level.

The cooperative migration dynamics of particles correlates to the nature of hexatic-isotropic phase transition in 2D systems of corner-rounded hexagons.

In the two-dimensional (2D) melting transition of colloidal systems, the hexatic-isotropic (H-I) transition can be either first-order or continuous. However, how particle dynamics differs at the single-particle level during these two different melting transitions remains to be disclosed. In this work, by Brownian dynamics (BD) simulations, we have systematically studied the dynamic behavior of corner-rounded hexagons during the H-I transition, for a range of corner-roundness = 0.

Microdroplet-Based In Situ Characterization Of The Dynamic Evolution Of Amorphous Calcium Carbonate during Microbially Induced Calcium Carbonate Precipitation.

Amorphous calcium carbonate (ACC) plays an important role in microbially induced calcium carbonate precipitation (MICP), which has great potential in broad applications such as building restoration, CO sequestration, and bioremediation of heavy metals, etc. However, our understanding of ACC is still limited. By combining microscopy of cell-laden microdroplets with confocal Raman microspectroscopy, we investigated the ACC dynamics during MICP.

Lattice Induced Short-Range Attraction between Like-Charged Colloidal Particles.

We perform experiments and computer simulations to study the effective interactions between like-charged colloidal tracers moving in a two-dimensional fluctuating background of colloidal crystal. By a counting method that properly accounts for the configurational degeneracy of tracer pairs, we extract the relative probability of finding a tracer pair in neighboring triangular cells formed by background particles. We find that this probability at the nearest neighbor cell is remarkably greater than those at cells with larger separations, implying an effective attraction between the tracers.

Fabrication of patterned calcium carbonate materials through template-assisted microbially induced calcium carbonate precipitation.

Patterned calcium carbonate materials with controlled morphologies have broad applications in both environmental and engineering fields. However, how to fabricate such materials through environmental-friendly methods under ambient conditions is still challenging. Here, we report a green approach for fabricating patterned calcium carbonate materials.

Synthesis of anisotropic colloids with concave and convex structures.

Anisotropic colloidal particles with concave and convex structures are useful in both theoretical studies and applications. In this work, we mass-produced polystyrene (PS) colloidal particles with multiple concavities through dispersion polymerization techniques. By increasing the delayed feeding time of the cross-linker divinylbenzene (DVB), the morphological evolution of particles can be classified into two stages, during which the formation of different concavities is consistent with either the buckling mechanism or phase separation mechanism.

Curvature-assisted self-assembly of Brownian squares on cylindrical surfaces.

Hypothesis: We hypothesize that curved surfaces, including cylindrical surfaces, which go beyond prior experiments using flat surfaces, can significantly influence and alter the phase behavior and self-assembly of dense two-dimensional systems of Brownian colloids.

Experiments: Here, we report a first experimental study regarding the self-assembly of Brownian square platelets with an edge length L = 2.3 μm on cylindrical surfaces having different curvatures; these platelets are subjected to a depletion attraction in order to form a monolayer above the cylindrical surface, yet have nearly hard interactions within the monolayer.

The Curvature Effect on the Diffusion of Single Brownian Squares on a Cylindrical Surface in the Presence of Depletion Attractions.

The diffusion of single micron-sized Brownian square platelets on cylindrical surfaces with different radii of curvature in the presence of depletion attractions was studied experimentally by video microscopy. The translational motion of a square is found to be diffusive along the axial direction of the cylinder but sub-diffusive along the circumferential direction due to the confinement induced by gravity, while its rotational motion displays a sub-diffusive behavior due to the confinement induced by orientation-dependent depletion attractions. Such a confinement effect decreases as the radius of curvature increases and can be tuned both through surface curvatures and/or depletion attractions.

A simple, switchable pili-labelling method by plasmid-based replacement of pilin.

Labelling of Type IV pili (TFP) can greatly improve our understanding of the pivotal roles of TFP in a variety of bacterial activities including motility, surface sensing and DNA-uptake etc. Here we show a simple and switchable pili-labelling method by plasmid-based inducible replacement of PilA without genetic modification in bacterial genome employed by complicated methods. Using this method, we characterized pili morphology and twitching motility of Pseudomonas aeruginosa in details.

Dynamic heterogeneity flow promotes binding reactions in a dense system of hard annular sector particles.

We perform molecular dynamics simulations on a system of hard annular sector particles (ASPs) to investigate the reaction-dynamics relationship. The dimerization reaction zone, mixing reaction zone including dimerization and n-merization (n > 2), and arrested region are observed successively as area fraction φ increases from low to high. In this work, we focus on the properties of the concentrated arrested region (φ≥ 0.

Universal Scaling Law for Colloidal Diffusion in Complex Media.

Using video microscopy and simulations, we study the diffusion of probe particles in a wide range of complex backgrounds, both crystalline and disordered, in quasi-2D colloidal systems. The dimensionless diffusion coefficients D^{*} from different systems collapse to a single master curve when plotted as a function of the structural entropy of the backgrounds, confirming the universal relation between diffusion dynamics and the structure of the medium. A new scaling equation is proposed with consideration for the viscous friction from the solvent, which is absent in previous theoretical models.

Vibrational Modes and Dynamic Heterogeneity in a Near-Equilibrium 2D Glass of Colloidal Kites.

Using video microscopy and particle-tracking techniques developed for dense Brownian systems of polygons, we study the structure-dynamics relationship in a near-equilibrium 2D glass consisting of anisotropic Penrose kite-shaped colloids. Detailed vibrational properties of kite glasses, both translational and rotational, are obtained using covariance matrix techniques. Different from other colloidal glasses of spheres and ellipsoids, the vibrational modes of kite glasses at low frequencies show a strong translational character with spatially localized rotational modes and extended translational modes.

In Situ Real-Time Study on Dynamics of Microbially Induced Calcium Carbonate Precipitation at a Single-Cell Level.

Ureolytic microbially induced calcium carbonate precipitation (MICP) is a promising green technique for addressing a variety of environmental and architectural concerns. However, the dynamics of MICP especially at the microscopic level remains relatively unexplored. In this work, by applying a bacterial tracking technique, the growth dynamics of micrometer-sized calcium carbonate precipitates induced by Sporosarcina pasteurii were studied at a single-cell resolution.

Induced Attraction between Polystyrene Colloidal Particles in a Binary Mixture with PNIPAM Colloidal Microgels.

We investigate the phase behaviors of binary mixtures of polystyrene (PS) hard-sphere and poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAM) soft-sphere colloidal particles as a function of temperature. As the temperature increases, apparent attractions arise between the PS particles, to the point of clustering at the highest temperature. This attractive force is found to be due to the change in pH caused by the acrylic acid co-polymerized with the temperature-sensitive PNIPAM particles, which in turn collapses the sterical stabilizing surface layers on the PS particles.

Asymmetrical phase separation and gelation in binary mixtures of oppositely charged colloids.

Two types of colloidal particles, which are nearly the same in chemical composition but carry opposite surface charges, are mixed in water. Depending on the relative proportion of the oppositely charged particles, the process of aggregation leads to the formation of discrete clusters of various sizes in dilute dispersions, and to the development of particle gel networks in more concentrated systems. Due to the significant difference in the absolute values of surface charges (negative particle: -48 mV, positive particle: +24 mV), the phase separation and the gelation behaviors are asymmetric with respect to the mixing ratio.

An Optically Driven Bistable Janus Rotor with Patterned Metal Coatings.

Bistable rotation is realized for a gold-coated Janus colloidal particle in an infrared optical trap. The metal coating on the Janus particles are patterned by sputtering gold on a monolayer of closely packed polystyrene particles. The Janus particle is observed to stably rotate in an optical trap.

Differentiating bonding and caging in a charged colloid system through rheological measurements.

The linear and nonlinear rheological measurements were utilized to study the mechanical response of concentrated mixtures of colloidal particles with opposite charges. The particle volume fraction (Φ) spans the region from low volume fraction (Φ = 0.18) gel to high volume fraction (Φ = 0.