Chain Collapse Research Articles

Effect of shear rate, temperature, and salts on the viscosity and viscoelasticity of semi‐dilute and entangled xanthan gum

AbstractXanthan gum, a naturally‐occurring, high‐molecular‐weight, anionic polyelectrolyte, exhibits significant drag‐reducing properties at low concentrations in water, suggesting promising applications in geothermal networks. The flow behavior of xanthan solutions are explored, specifically at concentrations in the semi‐dilute (1000 ppm by mass) and entangled (4000 ppm) regimes as well as in both water and various salt solutions across a temperature range of 5–85°C. The viscosity and viscoelastic properties of xanthan solutions examine relationships between polyelectrolyte concentration, temperature, and salt concentration. Viscosity decreases by two orders of magnitude in 4000 ppm xanthan solutions in deionized water and with 50 mM NaCl (in the high salt limit) as the temperature increases from 5 to 85°C. Next, the addition of salts affects viscosity differently in the two concentration regimes. Specifically, at 25°C, the zero‐shear rate viscosity upon salt addition decreases by 63% for 1000 ppm solutions (from 0.54 to 0.2 Pa s) but increases by 280% for 4000 ppm solutions (from 28 to 107 Pa s). At 1000 ppm, salt ions cause chain collapse, reducing viscosity; At 4000 ppm, entanglements led to structural changes, resulting in higher viscosity. Furthermore, three salts commonly found in geothermal waters, namely NaCl, Na2CO3, and NaHCO3, exhibited similar changes in viscosity and shear thinning behavior in the entangled regime across temperatures from 5 to 85°C.

Do Tensions in the South China Sea Herald the Collapse of Global Supply Chains?

It is now widely recognized that geopolitical tensions disrupt global supply chains, complicating trade flows and increasing the risk associated with logistics operations. The South China Sea, a strategic and disputed region of the world, is a perfect illustration of the stakes involved in these disruptions. Situated between several Asian countries, the region is crucial to world trade, but is subject to territorial conflicts, notably between China and Taiwan. Its increasing militarization and abundance of natural resources exacerbate geopolitical tensions, given that the South China Sea is vital for the transportation of goods, linking Asian, European and American markets. My speculative paper looks at the possible collapse of certain global value chains under the pressure of geopolitical tensions, leading to the emergence of a logistically multipolar planet.

Proposal and parametric investigations of square steel tubes as post-tensioned connectors for linear-shaped precast concrete elements

Given the pivotal role of connections in the progress of the precast building industry, issues such as costs, chain collapse, and low robustness in all degrees of freedom are critical considerations. This study draws inspiration from Concrete Filled Steel Tube Elements to design and investigate using simple steel tubes as joints for precast linear-shaped elements. The study proposes and examines uncomplicated joints where two precast reinforced concrete beams are positioned within the tube. The encompassment of the beams by the tube, combined with the application of post-tensioning forces, creates a sturdy integrity between the beams, resembling a head-to-head joint. Through 48 experimental tests, various connection parameters such as beam and tube cross-section height, re-bar quantity, tube thickness, and length were systematically investigated. The experimental setup utilized a three-point bending-shear testing configuration, and the results were compared with monolithic references. The findings demonstrate that these adaptive and ductile connections rapidly exhibit a capacity similar to that of monolithic exact beams. All studied parameters exhibited their influences on the capacity of the connection; however, the primary determinant is the length of the tube. Within the discussed range, the tube length should be at least twice as long as the height of the beam. Failing to meet this criterion would prevent the complete manifestation of the desired failure mechanism.

Model of the “Economic Cross” of the Digital Platform: Opportunities and Conditions for Interindustry Technological Convergence

The platform economy is an objective stage in the evolution of the digital economy, whose development is carried out under the influence of the trend of involving a large number of SMEs and individuals in economic relations as their direct participants. Unlike the pre-digital era, when operational commercial direct interaction between small participants in economic relations turned out to be impossible, communication technologies of the second decade of the 21st century have created favorable opportunities for the development of independent businesses of individuals and small professional teams. The process of commercialization of household resources is actively taking place in the form of the development of private blogs as platforms for commercial advertising and mutual trade of goods and services by individuals online, which creates a direct competitive threat to traditional trading companies. The current stage in the development of online participation of SMEs and individuals in commercial relations is the development of outsourcing relationships, within which part of the processes implemented by large businesses independently using hired personnel and their own infrastructure will be delegated to independent network structures on a competitive basis. At the same time, in proportion to the growing popularity of e-commerce, public demands for the security of such transactions are increasing, which is especially important in conditions of sanctions uncertainty and high risks of supply chain collapse. This circumstance determines the business request for systematization of the digital space and its centralization, the terminal stage of which is an inter-industry digital platform. The purpose of the scientific article is to develop a system of proposals for the formation of a national intersectoral outsourcing platform based on the “economic cross” model. A system of innovative solutions has been developed regarding the organization of economic interaction between subjects, the procedure for financing the activities of the platform by its participants, and the distribution of indirect industry income arising from the functioning of the platform.

Effect of the Protein Chain Conformation on the Collapse into Nanoparticles.

Protein single-chain nanoparticles can outperform synthetic nanoparticles in biomedical applications due to enhanced biocompatibility. Compared to synthetic (co)polymers, the chemical complexity of proteins challenges chain conformation control. Here, we investigate the impact of the precursor chain conformation of bovine serum albumin (BSA) on the nanoparticle structure after intramolecular cross-linking. We explore the urea concentration (denaturant), pH, salt, cross-linker length, and concentration. Small-angle neutron scattering and dynamic light scattering experiments reveal a shrinking chain conformation upon cross-linking. However, the ability to collapse depends on solvent conditions: more expanded chains collapse more, whereas proteins that are already compact barely change in size upon cross-linking. Static light scattering measurements demonstrate that binding is primarily intramolecular. The use of a shorter cross-linker does not lead to collapse of extended chains. Overall, BSA exhibits a similar behavior to that of polymer nanoparticles, which then allows to harness the precursor conformation for morphological control.

Spectroscopic and solution properties characterization of quaternary ammonium ion containing polycations complexed with fluorescent rhodamine sulfonic acid dyes

Based on the growing range of applications for polycations in research and commercial materials, a continuing need exists to advance the fundamental knowledge and understanding of this class of materials. Spectroscopic and solution properties characterizations of noncovalently labeled, fluorescent Alexa Fluor® dye complexes of two commercial polycations, poly(2-(trimethylamino) ethyl methacrylate) monocation and poly[bis[2-chloroethyl] ether-alt-1,3-bis[3-(dimethylamino) propyl] urea] dication are reported to help address this need. A variety of fluorescence spectroscopic methods are used with a special emphasis on fluorescence correlation spectroscopy (FCS) which is applied to characterize the Stokes radius (RS) and equilibrium dissociation constants (Kd) of dye-polycation complexes at nanomolar dye concentrations. Resulting RS values indicate dye binding to individual polycation chains. Measured Kd values in the sub-micromolar range are consistent with strong dye binding. Increasing solution ionic strength with sodium chloride addition inhibits dye binding and decreases the RS of dye-polycation complexes due to size collapse of polycation chains. The complexes differ in their solution stability to ionic strength changes suggesting that both electrostatic and hydrophobic binding interactions influence dye binding. This study establishes the viability of noncovalent dye-polycation complexation in concert with FCS characterization as a general approach for investigating the properties of quaternary ammonium ion containing polycations in aqueous solution.

How specific ion effects influence the mechanical behaviors of amide macromolecules? A cross-scale study.

The mechanisms of specific ion effects on the properties of amide macromolecules is essential to understanding the evolution of life. Because most biological macromolecules contain both complex hydrophilic and hydrophobic structures, it is challenging to accurately identify the contributions of molecular structure to macroscopic behaviors. Herein, we investigated the influence of specific ion effects on the mechanical behaviors of poly(N-isopropylacrylamide) and neutral polyacrylamide (i.e., PNIPAM and NPAM), through a cross-scale study that includes single-molecule force spectroscopy, molecular dynamics simulation and macro mechanical method. The results indicate that the molecular conformation can be markedly influenced by the hydrophilicity (or hydrophobicity) of both macromolecule chain and ions. An extended chain conformation can be obtained when the side groups and ions are relatively hydrophilic, which can also increase the elasticity of a macromolecule chain and film materials. The relatively hydrophobic components promote the collapse of macromolecule chains and reduce the molecular elasticity. It is believed that the hydrogen bonding intensity between a macromolecule chain and aquated ions controls the chain conformation and the elasticity of molecules and films. This study is not only helpful for understanding the self-assembly mechanism of organisms but also provides a way to associate the molecular properties with the macroscopic performance of materials.

Analysis of progressive collapse disaster and its anchoring effectiveness in jointed rock tunnel

AbstractThe complexity and variability of the structural distribution and combination characteristics of jointed rock masses make the response mechanism of tunnel rock collapse different, and there is a lack of systematic research on the existing perimeter rock instability mode and bolt support scheme. Based on numerical simulations of the block system structure of a nodular rock mass, the existing theory of bolt support is compared and analyzed to explore the scope of their respective applications. Combined with the spatial and temporal transport law of block instability, a new batch instability model of jointed rock tunnels is proposed, which reveals the progressive collapse catastrophe evolution mechanism of a collapsed interlocking block system after the instability of the key blocks and elucidates the coupling mechanism between the bolts and the block system structure as well as their anchoring effectiveness. Finally, for the actual tunnel project, the instability batches of the surrounding rock are identified, and the corresponding optimized design of the bolt support is presented, which has achieved good support effects. The research results can provide important theoretical guidance and practical engineering value for risk avoidance, disaster identification and targeted prevention and control of dangerous rock fall and chain collapse instability disasters in jointed rock body tunnels.

Wetting-induced collapse of loess: Tracing microstructural evolution

Loess is a silt-dominated, clastic yellow-to-yellowish brown aeolian sediment with high porosity and low density. The metastable microstructure of loess makes it highly susceptible to collapse, which plays a major role in landform evolution, geohazard development and engineering damages, particularly the widespread occurrences of settlement, deformation and cracking of civil engineering structures. Differing from the existing investigations based on pre- and post-collapse comparison, the present study is to report the microstructural changes during the collapse process and to determine how each microstructural constitutive element participates in this process. A series of laboratory tests was conducted on undisturbed loess specimens to simulate and capture snapshots of microstructure at five representative points during the entire collapse process. Results show that the loess microstructure becomes more homogeneous as the outstanding macropores are crushed into smaller (meso- and mini-pores) pores, the number of pores is dramatically increased, and the pore throats become narrower. The pore shapes have no obvious changes and remain elongated and rough-edged morphology from the point of view of statistic. Regarding solids, the pre-collapse unstable point-to-point contacts tend to transform into relatively stable edge (edge-edge or point-edge) type contacts, whilst coarse particles tend to reorient along the horizonal direction. XRD, SEM and EDS analysis indicates that these changes in the nature and distribution of pores and particles result from (1) the breakage and disintegration of moderately to highly weathered particles, (2) the disintegration of the matrix due to the swelling of clay minerals and the dissolution of calcium carbonates, (3) the consequential modifications of the microscopic forces which lead to slipping, rotation and therefore dislocation of particles, and (4) the collapse of mesoscale force chains along particles, reforming on smaller scales with larger numbers, shorter lengths and horizontal alignments.

Surface Orthogonal Patterning and Bidirectional Self-Assembly of Nanoparticles Tethered by V-Shaped Diblock Copolymers.

We investigated the surface orthogonal patterning and bidirectional self-assembly of binary hairy nanoparticles (NPs) constructed by uniformly tethering a single NP with multiple V-shaped AB diblock copolymers using Brownian dynamics simulations in a poor solvent. At low concentration, the chain collapse and microphase separation of binary polymer brushes can lead to the patterning of the NP surface into A- and B-type orthogonal patches with various numbers of domains (valency), n = 1-6, that adopt spherical, linear, triangular, tetrahedral, square pyramidal, and pentagonal pyramidal configurations. There is a linear relationship between the valency and the average ratio of NP diameter to the polymers' unperturbed root-mean-square end-to-end distance for the corresponding valency. The linear slope depends on the grafting density and is independent of the interaction parameters between polymers. At high concentration, the orthogonal patch NPs serve as building blocks and exhibit directional attractions by overlapping the same type of domains, resulting in self-assembly into a series of fascinating architectures depending on the valency and polymer length. Notably, the 2-valent orthogonal patch NPs have the bidirectional bonding ability to form the two-dimensional (2D) square NP arrays by two distinct pathways. Simultaneously patching A and B blocks enables the one-step formation of 2D square arrays via bidirectional growth, whereas step-by-step patching causes the directional formation of 1D chains followed by 2D square arrays. Moreover, the gap between NPs in the 2D square arrays is related to the polymer length but independent of the NP diameter. These 2D square NP arrays are of significant value in practical applications such as integrated circuit manufacturing and nanotechnology.

How hydrophobicity, side chains, and salt affect the dimensions of disordered proteins.

Despite the generally accepted role of the hydrophobic effect as the driving force for folding, many intrinsically disordered proteins (IDPs), including those with hydrophobic content typical of foldable proteins, behave nearly as self-avoiding random walks (SARWs) under physiological conditions. Here, we tested how temperature and ionic conditions influence the dimensions of the N-terminal domain of pertactin (PNt), an IDP with an amino acid composition typical of folded proteins. While PNt contracts somewhat with temperature, it nevertheless remains expanded over 10-58°C, with a Flory exponent, ν, >0.50. Both low and high ionic strength also produce contraction in PNt, but this contraction is mitigated by reducing charge segregation. With 46% glycine and low hydrophobicity, the reduced form of snow flea anti-freeze protein (red-sfAFP) is unaffected by temperature and ionic strength and persists as a near-SARW, ν ~ 0.54, arguing that the thermal contraction of PNt is due to stronger interactions between hydrophobic side chains. Additionally, red-sfAFP is a proxy for the polypeptide backbone, which has been thought to collapse in water. Increasing the glycine segregation in red-sfAFP had minimal effect on ν. Water remained a good solvent even with 21 consecutive glycine residues (ν > 0.5), and red-sfAFP variants lacked stable backbone hydrogen bonds according to hydrogen exchange. Similarly, changing glycine segregation has little impact on ν in other glycine-rich proteins. These findings underscore the generality that many disordered states can be expanded and unstructured, and that the hydrophobic effect alone is insufficient to drive significant chain collapse for typical protein sequences.

Degradable, anti-swelling, high-strength cellulosic hydrogels via salting-out and ionic coordination

Cellulosic hydrogels are widely used in various applications, as they are natural raw materials and have excellent degradability. However, their poor mechanical properties restrict their practical application. This study presents a facile approach for fabricating cellulosic hydrogels with high strength by synergistically utilizing salting-out and ionic coordination, thereby inducing the collapse and aggregation of cellulose chains to form a cross-linked network structure. Cellulosic hydrogels are prepared by soaking cellulose in an Al2(SO4)3 solution, which is both strong (compressive strength of up to 16.99 MPa) and tough (compressive toughness of up to 2.86 MJ/m3). The prepared cellulosic hydrogels exhibit resistance to swelling in different solutions and good biodegradability in soil. The cellulosic hydrogels are incorporated into strain sensors for human-motion monitoring by introducing AgNWs. Thus, the study offers a promising, simple, and scalable approach for preparing strong, degradable, and anti-swelling hydrogels using common biomass resources with considerable potential for various applications.

Impact of Corporate Social Responsibility on Operations of a Live-Streaming Supply Chain

Corporate social responsibility (CSR) is widely noticed as an essential tool for business operation and sustainable development. Meanwhile, the fiercely competitive external environment and unpredictable events prompt enterprises’ cooperation to prevent supply chain collapse. We investigate the cooperative strategy in a live-streaming supply chain (LSC) consisting of a dominant brand owner, a retailer, and a live streamer, where the brand owner considers CSR by considering the welfare of stakeholders. We construct one non-cooperative and three cooperative Stackelberg game models to explore the impact of CSR on cooperative strategy and LSC operations. The results show the following. (1) When the brand owner considers CSR, LSC members and systems are more profitable in the four models than when the brand owner does not consider CSR. (2) When the flow effect is small, the brand owner tends to cooperate with the retailer; otherwise, the brand owner prefers to cooperate with the live streamer. (3) The grand coalition C (the brand owner cooperates with the retailer and live streamer) is the consistent strategy for the LSC system, consumers, and society. These findings help enterprises recognize the importance of CSR and collaboration, thus further providing reference opinions on engaging in CSR and how to achieve collaboration.

Entropy-driven polymer collapse on increasing the temperature: The case of poly(N-vinylcaprolactam)

Poly(N-vinylcaprolactam), PNVCL, chains undergo a temperature-induced, reversible and endothermic collapse in water at around 32 °C. The entropy gain driving PNVCL collapse has to come from water molecules, but it cannot be associated with their passage from the polymer hydration shell to the bulk because there is no difference in their tetrahedral structural order. I have shown that the water entropy gain comes from the decrease in solvent-excluded volume effect associated with chain collapse: there is a marked increase in the spatial configurations accessible to water molecules, leading to a large gain in their translational entropy. This mechanism, even though generic, proves to be effective solely in water and aqueous solutions because the magnitude of the solvent-excluded volume effect is amplified by the large number density of water, stemming from the strength of H-bonds and the small size of water molecules.

Tailoring Hierarchical Structure and Rare Earth Affinity of Compositionally Identical Polymers via Sequence Control.

Macromolecule sequence, structure, and function are inherently intertwined. While well-established relationships exist in proteins, they are more challenging to define for synthetic polymer nanoparticles due to their molecular weight, sequence, and conformational dispersities. To explore the impact of sequence on nanoparticle structure, we synthesized a set of 16 compositionally identical, sequence-controlled polymers with distinct monomer patterning of dimethyl acrylamide and a bioinspired, structure-driving di(phenylalanine) acrylamide (FF). Sequence control was achieved through multiblock polymerizations, yielding unique ensembles of polymer sequences which were simulated by kinetic Monte Carlo simulations. Systematic analysis of the global (tertiary- and quaternary-like) structure in this amphiphilic copolymer series revealed the effect of multiple sequence descriptors: the number of domains, the hydropathy of terminal domains, and the patchiness (density) of FF within a domain, each of which impacted both chain collapse and the distribution of single- and multichain assemblies. Furthermore, both the conformational freedom of chain segments and local-scale, β-sheet-like interactions were sensitive to the patchiness of FF. To connect sequence, structure, and target function, we evaluated an additional series of nine sequence-controlled copolymers as sequestrants for rare earth elements (REEs) by incorporating a functional acrylic acid monomer into select polymer scaffolds. We identified key sequence variables that influence the binding affinity, capacity, and selectivity of the polymers for REEs. Collectively, these results highlight the potential of and boundaries of sequence control via multiblock polymerizations to drive primary sequence ensembles hierarchical structures, and ultimately the functionality of compositionally identical polymeric materials.

Higher education response to institutional upheaval: Outcomes of industry collaborations during the COVID-19 pandemic

Institutional upheaval spurred by the COVID-19 crisis suddenly and dramatically transformed the rules of the game for higher education organizations. The global pandemic thrust colleges and universities into ambiguous institutional environments. Disruption of established routines and supply networks resulted in the near collapse of global supply chains providing personal protective equipment (PPE), particularly N95 masks, needed by healthcare workers on the medical frontlines. This study describes and analyzes higher education and industry (HEI) partnership collaborations that adapted rapidly and responded effectively to meet the critical PPE need. The Citadel, Military College of South Carolina (The Citadel), along with the Tommy and Victoria Baker School of Business (BSB) and its Innovation Lab., engaged in a partnership with medical professionals at the Medical University of South Carolina (MUSC). This partnership successfully manufactured, assembled, and distributed one thousand 3D-printed N95 masks in a crucial 16-week period. The study also shows how organizations in both institutional fields were able to expand dynamic capabilities enabling them to sense opportunities and to seize them by engaging and supporting each other in rapid and effective resource reconfigurations. This HEI collaboration culminated in a memorandum of understanding for ongoing collaboration to develop innovations for future responses to healthcare challenges.

Effects of Drug Conjugation on the Biological Activity of Single-Chain Nanoparticles.

The field of single-chain nanoparticles (SCNPs) continues to mature, and an increasing range of reports have emerged that explore the application of these small nanoparticles. A key application for SCNPs is in the field of drug delivery, and recent work suggests that SCNPs can be readily internalized by cells. However, limited attention has been directed to the delivery of small-molecule drugs using SCNPs. Moreover, studies on the physicochemical effects of drug loading on SCNP performance is so far missing, despite the accepted view that such small nanoparticles should be significantly affected by the drug loading content. To address this gap, we prepared a library of SCNPs bearing different amounts of a covalently conjugated therapeutic drug-sulfasalazine (SSZ). We evaluated the impact of the conjugated drug loading on both the synthesis and biological activity of SCNPs on pancreatic cancer cells (AsPC-1). Our results reveal that covalent drug conjugation to the side chains of the SCNP polymer precursor interferes with chain collapse and cross-linking, which demands optimization of reaction conditions to reach high degrees of cross-linking efficiencies. Small-angle neutron scattering and diffusion-ordered spectroscopy nuclear magnetic resonance (DOSY NMR) analyses reveal that SCNPs with a higher drug loading display larger sizes and looser structures, as well as increased hydrophobicity associated with a higher SSZ content. Increased SSZ loading led to reduced cellular uptake when assessed in vitro, whereby SCNP aggregation on the surface of AsPC-1 cells led to reduced toxicity. This work highlights the effects of drug loading on the drug delivery efficiency and biological behavior of SCNPs.

Förster resonance energy transfer within single chain nanoparticles.

Single chain nanoparticles (SCNPs) are a highly versatile polymer architecture consisting of single polymer chains that are intramolecularly crosslinked. Currently, SCNPs are discussed as powerful macromolecular architectures for catalysis, delivery and sensors. Herein, we introduce a methodology based on Förster Resonance Energy Transfer (FRET) to evidence the folding of single polymer chains into SCNPs via fluorescence readout. We initially introduce a molecular FRET pair based on a bimane and nitrobenzoxadiazole (NBD) moiety and study its fluorescence properties in different solvents. We subsequently construct a low dispersity polymer chain carrying NBD units, while exploiting the bimane units for intramolecular chain collapse. Upon chain collapse and SCNP formation - thus bringing bimane and NBD units into close proximity - the SCNPs report their folded state by a strong and unambiguous FRET fluorescence signal. The herein introduced reporting of the folding state of SCNPs solely relies on an optical readout, opening avenues to monitoring SCNP folding without recourse to complex analytical methodologies.

Tuning the nanoparticles internal structure: fluorinated single-chain nanoparticles (SCNPs) generated by chain collapse of random copolymers

The generation of nanosized compartments in single chain nanoparticles (SCNPs) is a promising approach to generate individualized confinement-zones on a small scale for drug-encapsulation or catalysis. We here report the...

Moisture Absorbing and Water Self‐Releasing from Hybrid Hydrogel Desiccants

AbstractAtmospheric moisture is a valuable resource for fresh water and potentially sustainable energy. However, direct harvesting water from moisture (the vapor form) remains the most challenging. Hybrid desiccants made from hydrogels embedded with salt offer promise in absorbing moisture. However, the desorption process often requires additional energy to heat the samples. Here, poly(acrylic acid) (PAA) hydrogels embedded with lithium chloride are prepared, demonstratng simultaneous moisture absorption and self‐release of liquid water at room temperature with 50–90% relative humidity. The water self‐releasing process can be separated into two distinct stages: 1) surface release, where water droplets grow on the hydrogel surface due to differences in nucleation and diffusion rates, and 2) bulk release, triggered by the collapse of polymer chains, subsequently releasing water from the hydrogel network. Factors such as salt concentration, hydrogel crosslinking density, and film thickness are investigated to better understand the moisture absorption and water‐releasing processes. Moreover, hydrophobic domains are introduced onto the salt‐embedded PAA films, creating an edge effect that enhances the droplet growth rates. When the hydrophobic domains are patterned, the movement of released water can be guided, resulting in a threefold increase in water removal rate attributed to gravitational force.