Experiments show that macromolecular crowding modestly reduces the size of intrinsically disordered proteins (IDPs) even at volume fraction (φ) similar to that in the cytosol whereas DNA undergoes a coil-to-globule transition at very small φ. We show using a combination of scaling arguments and simulations that the polymer size Rg(φ) depends on x = Rg(0)/D where D is the φ-dependent distance between the crowders. If x < ∼ O(1), there is only a small decrease in Rg(φ) as φ increases. When x O(1), a cooperative coil-to-globule transition is induced. Our theory quantitatively explains a number of experiments.The importance of crowding in biology is being increasingly appreciated because of the realization that cellular processes occur in a dense medium containing polydisperse mixture of macromolecules. A number of studies have been performed to understand the role crowding particles play in inducing structural transitions in disordered chiral homopolymers [1,2], in protein [3][4][5] and RNA folding [6][7][8], gene regulation through DNA looping [9], genome compaction [10]. Some of the consequences of crowding can be qualitatively explained using depletion interaction introduced by Asakura and Oosawa (AO) [11]. In the AO picture, the crowding particles, treated as hard objects, vacate the interstitial space in the interior of the macromolecule to maximize their entropy. As a result, an osmotic pressure due to crowders reduces the size of the macromolecule.The predictions based on the AO theory rationalize the impact of crowding effects on synthetic and biological polymers qualitatively provided only excluded volume interactions between the crowding particles and the macromolecules dominate. Even in this limit two questions of particular importance for experiments on biopolymers require scrutiny. (i) What is the extent of crowding-induced compaction in finite-sized polymer coils? These systems are minimal models for unfolded and intrinsically disordered proteins (IDPs), and in some limits (random loop model) also provide a useful caricature of chromosome folding. (ii) For polymers with N monomers, what is the dependence of the average radius of gyration, R g (φ) (≡ R 2 g (φ)1/2 ), as a function of the volume fraction φ and size of the crowders? It is important to answer these questions quantitatively to resolve seemingly contradictory conclusions reached in recent experiments.Here, we answer these questions using a combination of scaling arguments and computer simulations. The two length scales that determine the degree of polymer compaction in solution, with crowding particles interacting with each other and the polymer via hard repulsions, are R g (0) (the size of the coil at φ = 0), and the average distance D between the crowders. We propose a scaling relation to predict the dependence of R g (φ) on φ based on the expectation that when D < ∼ R g (0) the osmotic pressure acting on the polymeric chain should reduce the polymer size. If correlations between the crowding particles are negligible, as explicitly shown h...

The preparation of ferroelectric polymer–metallic nanowire composite nanofiber triboelectric layers is described for use in high‐performance triboelectric nanogenerators (TENGs). The electrospun polyvinylidene fluoride (PVDF)–silver nanowire (AgNW) composite and nylon nanofibers are utilized in the TENGs as the top and bottom triboelectric layers, respectively. The electrospinning process facilitates uniaxial stretching of the polymer chains, which enhances the formation of the highly oriented crystalline β‐phase that forms the most polar crystalline phase of PVDF. The addition of AgNWs further promotes the β‐phase crystal formation by introducing electrostatic interactions between the surface charges of the nanowires and the dipoles of the PVDF chains. The extent of β‐phase formation and the resulting variations in the surface charge potential upon the addition of nanowires are systematically analyzed using X‐ray diffraction (XRD) and Kelvin probe force microscopy techniques. The ability of trapping the induced tribocharges increases upon the addition of nanowires to the PVDF matrix. The enhanced surface charge potential and the charge trapping capabilities of the PVDF–AgNW composite nanofibers significantly enhance the TENG output performances. Finally, the mechanical stability of the electrospun nanofibers is dramatically enhanced while maintaining the TENG performances by applying thermal welding near the melting temperature of PVDF.

Recent experiments showing scaling of the intrachromosomal contact probability, P (s) ∼ s −1 with the genomic distance s, are interpreted to mean a self-similar fractal-like chromosome organization. However, scaling of P (s) varies across organisms, requiring an explanation. We illustrate dynamical arrest in a highly confined space as a discriminating marker for genome organization, by modeling chromosome inside a nucleus as a homopolymer confined to a sphere of varying sizes. Brownian dynamics simulations show that the chain dynamics slows down as the polymer volume fraction (φ) inside the confinement approaches a critical value φc. The universal value of φ ∞ c ≈ 0.44 for a sufficiently long polymer (N 1) allows us to discuss genome dynamics using φ as a single parameter. Our study shows that the onset of glassy dynamics is the reason for the segregated chromosome organization in human (N ≈ 3 × 10 9 , φ φ ∞ c ), whereas chromosomes of budding yeast (N ≈ 10 8 , φ < φ ∞ c ) are equilibrated with no clear signature of such organization.

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The tuning of lateral and vertical correlations in self-organized PbSe/Pb 1-xEu xTe quantum dot superlattices by changes in the spacer thicknesses is demonstrated and shown to be due to finite size effects in the dot-dot interactions. As a consequence, different dot arrangements such as vertically aligned dot columns or fcc stacking are obtained for a single material system without changes in growth conditions. The different dot superstructures are shown to exhibit a different scaling behavior of the lateral versus vertical dot separation, as well as a different evolution of dot sizes and shapes.

We developed a method of chemically welding silver nanowires (AgNWs) using an aqueous solution containing sodium halide salts (NaF, NaCl, NaBr, or NaI). The halide welding was performed simply by immersing the as-coated AgNW film into the sodium halide solution, and the resulting material was compared with those obtained using two typical thermal and plasmonic welding techniques. The halide welding dramatically reduced the sheet resistance of the AgNW electrode because of the strong fusion among nanowires at each junction while preserving the optical transmittance. The dramatic decrease in the sheet resistance was attributed to the autocatalytic addition of dissolved silver ions to the nanowire junction. Unlike thermal and plasmonic welding methods, the halide welding could be applied to AgNW films with a variety of deposition densities because the halide ions uniformly contacted the surface or junction regions. The optimized AgNW electrodes exhibited a sheet resistance of 9.3 Ω/sq at an optical transmittance of 92%. The halide welding significantly enhanced the mechanical flexibility of the electrode compared with the as-coated AgNWs. The halide-welded AgNWs were successfully used as source-drain electrodes in a transparent and flexible organic field-effect transistor (OFET). This simple, low-cost, and low-power consumption halide welding technique provides an innovative approach to preparing transparent electrodes for use in next-generation flexible optoelectronic devices.

There exits strong correlation between the extended poly-glutamines (polyQ) within exon-1 of Huntingtin protein (Htt) and age onset of Huntington’s disease (HD), however, the underlying molecular mechanism is still poorly understood. Here we apply extensive molecular dynamics simulations to study the folding of Htt-exon-1 across five different polyQ-lengths. We find an increase in secondary structure motifs at longer Q-lengths, including β-sheet content that seems to contribute to the formation of increasingly compact structures. More strikingly, these longer Q-lengths adopt super-compact structures as evidenced by a surprisingly small power-law scaling exponent (0.22) between the radius-of-gyration and Q-length that is substantially below expected values for compact globule structures (~0.33) and unstructured proteins (~0.50). Hydrogen bond analyses further revealed that the super-compact behavior of polyQ is mainly due to the “glue-like” behavior of glutamine’s sidechains with significantly more sidechain-sidechain H-bonds than regular proteins in the Protein Data Bank (PDB). The orientation of the glutamine sidechains also tend to be “buried” inside, explaining why polyQ domains are insoluble on their own.

In the field of bionics, sophisticated and multifunctional electronic skins with a mechanosensing function that are inspired by nature are developed. Here, an energy-harvesting electronic skin (energy-E-skin), i.e., a pressure sensor with energy-harvesting functions is demonstrated, based on fingerprintinspired conducting hierarchical wrinkles. The conducting hierarchical wrinkles, fabricated via 2D stretching and subsequent Ar plasma treatment, are composed of polydimethylsiloxane (PDMS) wrinkles as the primary microstructure and embedded Ag nanowires (AgNWs) as the secondary nanostructure. The structure and resistance of the conducting hierarchical wrinkles are deterministically controlled by varying the stretching direction, Ar plasma power, and treatment time. This hierarchical-wrinkle-based conductor successfully harvests mechanical energy via contact electrification and electrostatic induction and also realizes self-powered pressure sensing. The energy-E-skin delivers an average output power of 3.5 mW with an open-circuit voltage of 300 V and a short-circuit current of 35 µA; this power is sufficient to drive commercial light-emitting diodes and portable electronic devices. The hierarchical-wrinkle-based conductor is also utilized as a self-powered tactile pressure sensor with a sensitivity of 1.187 mV Pa -1 in both contact-separation mode and the single-electrode mode. The proposed energy-E-skin has great potential for use as a next-generation multifunctional artificial skin, self-powered human-machine interface, wearable thin-film power source, and so on.