Carlos G. Lopez

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Verified

Carlos verified their affiliation via an institutional email.

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• PhD
• Professor (Assistant) at Pennsylvania State University

A comparative examination is presented of materials and approaches for the fabrication of microfluidic devices for small-angle neutron scattering (SANS). Representative inorganic glasses, metals, and polymer materials and devices are evaluated under typical SANS configurations. Performance criteria include neutron absorption, scattering background...

We report results of small angle neutron scattering measurements made on sodium polystyrene sulfonate in aqueous salt solutions. The correlation length (ξ) and osmotic compressibility are measured as a function of polymer (c) and added salt (c S) concentrations, and the results are compared with scaling predictions and the random-phase approximatio...

We report chain self-diffusion and viscosity data for sodium polystyrene sulfonate (NaPSS) in semidilute salt-free aqueous solutions measured by pulsed-field gradient NMR and rotational rheometry, respectively. The molecular weight of NaPSS is characterized using five techniques. Relationships between M w and the intrinsic viscosity and diffusion c...

We study the viscosity of polystyrenesulfonate with sodium and tetrabutylammonium counterions in aqueous and organic solvent media. We find that at low concentrations the Fuoss law (ηsp ∼ c1/2) is approximately obeyed, but at higher concentrations, an exponential dependence on the polymer volume fraction sets in. These findings are discussed in ter...

Understanding the influence of counterion and backbone solvation on the conformational and thermodynamic properties of polyelectrolytes in solution is one of the main open challenges in polyelectrolyte science. To address this problem, we study the scattering from semidilute solutions of a semiflexible polyelectrolyte, carboxymethyl cellulose (CMC)...

Polyelectrolytes often display good solubility in water but not in organic solvents, a feature that limits their applications in non-aqueous media such as hand-sanitisers. Here we show that this limitation can be overcome by tuning the counterion-solvent 1 affinity. To this end, the solubility and chain conformation of carboxymethylcellulose (CMC)...

We experimentally confirm a longstanding theoretical prediction of counterion-induced polyelec-trolyte collapse in low dielectric media. The scattering behaviour of polystyrene sulfonate in different solvents with dielectric permittivities in the range of ϵ ≃ 12 − 180 is investigated. For high and intermediate ϵ media, typical polyelectrolyte behav...

Tailoring polymer gel functionality by loading small molecules and nanoparticles is critical for drug delivery and tissue regeneration. Typically, solute loading in gels correlates with the degree of solvent swelling, which is controlled by the cross-link density and polymer/solvent interactions. However, the general assumption that the degree of s...

The nanometric ions (nano-ions) SiW12O404- (SiW) and B(C6H5)4- (BPh4) are considered as a superchaotropic and a hydro-phobic ion, respectively, in extension to the chaotropic side of the Hofmeister series. A distinction between chaotropic, superchaotropic and hydrophobic ions, however, has not been presented so far. Herein, we show by measurement o...

Understanding the influence of counterion and backbone solvation on the conformational and thermodynamic properties of polyelectrolytes in solution is one of the main open challenges in polyelectrolyte science. To address this problem, we study the scattering from semidilute solutions of a semiflexible polyelectrolyte, carboxymethyl cellulose (CMC)...

We study the conformational and flow properties of sodium polystyrenesulfonate in aqueous NaCl solutions in the high polymer, high added-salt region using rheology and small angle neutron scattering (SANS). For low salt concentrations, the specific viscosity decreases with added salt as expected. At very high salt, however, the specific viscosity i...

We study the conformational and flow properties of sodium polystyrene sulfonate in aqueous NaCl solutions in the high polymer, high added-salt region using rheology and small angle neutron scattering. For low salt concentrations, the specific viscosity decreases with added salt as expected. At very high salt however, the specific viscosity is found...

Polymers and rod-like colloids (PaRC) adopt a favorable orientation under sufficiently strong flows. However, how the flow kinematics affect the alignment of such nanostructures according to their extensibility remains unclear. By analyzing the shear- and extension-induced alignment of chemically and structurally different PaRC, we show that extens...

We study the conformational, conductometric and rheological properties of semiflexible polyelectrolyte carboxymethyl cellulose in mixtures of water and three non-solvents (ethanol, isopropanol and acetone). Small angle x-ray scattering measurements of the correlation length reveal that the local con-formation of the carboxymethyl chain is largely u...

We study the viscosity of polystyrene sulfonate with sodium and tetrabutylammonium counterions in aqueous and organic solvent media. We find that at low concentrations, the Fuoss law (ηsp ∼ c1/2) is approximately obeyed, but at higher concentrations an exponential dependence on the polymer volume fraction sets in. These findings are discussed in te...

Ionic-liquid gels, also known as ion gels, have gained considerable attention due to their high ionic conductivity and CO2 absorption capacity. However, their low mechanical strength has hindered their practical applications. A potential solution to this challenge is the incorporation of particles, such as silica nanoparticles, TiO2 nanoparticles,...

We investigate the phase behaviour and scattering properties of a polymerised ionic liquid (poly(1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide)) in 24 solvents of varying dielectric constants and solubility parameters. The polymer is found to be soluble in polar aprotic solvents and insoluble in non-polar or highly protic solvents....

Polymers and rod-like colloids (PaRC) adopt a favorable orientation under sufficiently strong flows. However, how the flow kinematics affect the alignment of such nanostructures according to their extensibility remains unclear. By analysing the shear-and extension-induced alignment of chemically and structurally different PaRC, we show that extensi...

Polyelectrolytes are a type of polymers possessing ionic groups on their repeating units. Since counterions can dissociate from the polymer backbone, polyelectrolyte chains are strongly influenced by the electrostatic interactions. As a result, the physical properties of polyelectrolyte solutions are significantly different from those of electrical...

We studied the viscosity of semidilute aqueous solutions of sodium polystyrenesulfonate as a function of polymer and salt concentrations. The viscosity data were quantified by applying a scaling relationship between solution correlation length ξ = lgν/B and number of monomers g per correlation volume for chains with monomer projection length l. The...

Polyelectrolytes are a class of polymers possessing ionic groups on their repeating units. Since counterions can dissociate from the polymer backbone, polyelectrolyte chains are strongly influenced by electrostatic interactions. As a result, the physical properties of polyelectrolyte solutions are significantly different from those of electrically...

Synergy between salt and sugar: Nanometric ions like Keggin polyoxometalates are revealed to induce the cross‐linking and hydrogel formation of polymeric sugars, namely non‐ionic cellulose ethers, as reported by Max Hohenschutz, Walter Richtering et al. in their Communication (DOI: 10.1002/ange.202210208). This novel gelation phenomenon exceeds the...

Nanometer‐sized anions (nano‐ions) like polyoxometalates and boron clusters exhibit so‐called superchaotropic behavior, which describes their strong binding to hydrated non‐ionic matter in water. We show here that nano‐ions, at millimolar concentrations, dramatically enhance the viscosity and induce gelation of aqueous solutions of non‐ionic cellul...

Synergy between salt and sugar: Nanometric ions like Keggin polyoxometalates are revealed to induce the cross‐linking and hydrogel formation of polymeric sugars, namely non‐ionic cellulose ethers, as reported by Max Hohenschutz, Walter Richtering et al. in their Communication (DOI: 10.1002/anie.202210208). This novel gelation phenomenon exceeds the...

Nanometer‐sized anions (nano‐ions) like polyoxometalates and boron clusters exhibit so‐called superchaotropic behavior, which describes their strong binding to hydrated non‐ionic matter in water. We show here that nano‐ions, at millimolar concentrations, dramatically enhance the viscosity and induce gelation of aqueous solutions of non‐ionic cellul...

Softness plays a key role in determining the macroscopic properties of colloidal systems, from synthetic nanogels to biological macromolecules, from viruses to star polymers. However, we are missing a way to quantify what the term "softness" means in nanoscience. Having quantitative parameters is fundamental to compare different systems and underst...

Functional microgels have powerful applications, especially due to their quick responsiveness to different external stimuli such as temperature, pH, ionic strength, solvent composition and light. Here, we describe the synthesis of novel dual-responsive poly(N-isopropylacrylamide) (PNIPAM) microgels and demonstrate that, in addition to temperature,...

Divalent ions are known to strongly influence the phase behavior, conformation, and flow properties of polyelectrolytes in solution. Here, we report small-angle neutron scattering and viscosity data for the magnesium salt of polystyrene sulfonate (MgPSS) in salt-free water and compare these results with analogous measurements for NaPSS. In a dilute...

The flow properties of ionic polysaccharides are determined by the interplay of electrostatic and hydrophobic interactions, which depend on the ionic strength and pH of the solvent. We explore the LVE and LAOS rheology of carboxymethyl cellulose (CMC) in aqueous media, focusing on its gelling behaviour. We find that addition of HCl promotes gel for...

Hydrogel microparticles (HMPs) find numerous practical applications, ranging from drug delivery to tissue engineering. Designing HMPs from the molecular to macroscopic scales is required to exploit their full potential as functional materials. Here, we explore the gelation of sodium carboxymethyl cellulose (NaCMC), a model anionic polyelectrolyte,...

Divalent ions are known to strongly influence the phase behaviour, conformation and flow properties of poly- electrolytes in solution. Here, we report small angle neutron scattering and viscosity data for the magnesium salt of polystyrene sulfonate (MgPSS) in salt-free water and compare these results with analogous measure- ments for NaPSS. In dilu...

The oscillatory rheology of a high molecular weight carboxymethyl cellulose sample with low degree of substitution (DS ≈ 0.7) is studied as a function of polymer concentration and electrolyte content. Beyond a polymer concentration of c ≈ 3 wt%, weak gels are formed. These display G' > G'' and a weak frequency dependence of both moduli over the ent...

We report results of small angle neutron scattering measurements made on sodium polystyrene sulfonate in aqueous salt solutions. The correlation length (ξ) and osmotic compressibility are measured as a function of polymer (c) and added salt (cS) concentrations, and the results are compared with scaling predictions and the random-phase approximation...

This is a research proposal that I submitted to the German Research Foundation (DFG) on October 2019 to apply for a Individual Research Grant. It outlines my planned research for the next few years. Writing the proposal was somewhat challenging. In contrast to research articles, where many good papers are available for reference, I did not have any...

We report chain self-diffusion and viscosity data for sodium polystyrene sulfonate (NaPSS) in semidilute salt-free aqueous solutions measured by pulsed field gradient NMR and rotational rheometry respectively. The observed concentration dependence of η and D are consistent with the Rouse-Zimm scaling model if the monomeric friction coefficient (ζ)...

We study the entanglement properties of flexible and semiflexible polyelectrolytes sodium polystyrene sulfonate and sodium carboxymehtyl cellulose. In dilute salt-free and excess-salt solutions these polymers adopt rod-like and expanded coil conformations respectively. The solvent’s ionic strength has a large impact on the conformation of polyelect...

We report a small-angle neutron scattering (SANS) study of semidilute aqueous solutions of sodium carboxymethyl cellulose (NaCMC), in the presence of mono- (Na+) and divalent salts (Mg2+, Ca2+, Zn2+, and Ba2+). A degree of substitution of 1.3 is selected to ensure that, in salt-free solution, the polymer is molecularly dissolved. We find that Na+ a...

We study the dilute solution properties and entangled dynamics of hydrox-ypropyl cellulose (HPC), a semiflexible polymer, in aqueous solution. Intrinsic viscosity data are consistent with a polymer in θ solvent with a Kuhn length of 22 nm. The overlap concentration, estimated as the reciprocal of the intrinsic viscosity scales with the degree of po...

Viscosity data for aqueous solutions of sodium carboxymethyl cellulose (NaCMC) as a function of polymer concentration (c), added salt concentration (cS), and degree of polymerization (N) are presented. In dilute solution, NaCMC adopts an expanded coil conformation in excess salt (R∝N0.59, [η]∼N0.786) and a rodlike conformation (R∝N, [η]∼N2) in salt...

Exploiting soft, adaptive microgels as building blocks for soft materials with controlled and predictable viscoelastic properties is of great interest for both industry and fundamental research. Here the flow properties of different poly(N-isopropylacrylamide) (pNIPAM) microgels are compared: regularly crosslinked versus ultra-low crosslinked (ULC)...

We study the rheological properties of sodium polystyrene sulfonate in salt-free and excess added salt solution. The overlap concentration scales as c* ∝ N−2 (DI water) and c* ∝ N−0.77 (excess salt), corresponding to rodlike and expanded coil conformations, respectively. A comparison of small-angle X-ray scattering and viscosity data reveals that c...

We study the dilute solution properties and entangled dynamics of hydroxypropyl cellulose (HPC), a semi-flexible polymer, in aqueous solution. Intrinsic viscosity data are consistent with a polymer in θ solvent with a Kuhn length 22 nm. The overlap concentration, estimated as the reciprocal of the intrinsic viscosity scales with the degree of polym...

We study the rheological properties of sodium polystyrene sulfonate in salt-free and excess added salt solution. The overlap concentration scales as c ≈ N^-2 (DI water) and c ≈ N^-0.77 (excess salt) corresponding to rod-like and expanded coil conformations respectively. A comparison of SAXS and viscosity data reveals that c* may be quantitatively e...

We report dynamic light scattering data for a PNIPAM based microgel copolymerised with 2% ionic groups. The hydrodynamic radius is measured as a function of temperature (which varies the solvent quality) and added salt concentration (cS) from salt-free conditions up to cS = 0.1 M. Incorporation of the ionic co-monomer leads to an increase of the vo...

We report viscosity data of non-entangled sodium polystyrene sulfonate (NaPSS) in salt-free aqueous solution as a function of polymer concentration (c) and degree of polymerisation (N). Different empirical equations are examined and found not describe the semidilute solution viscosity over a wide concentration range and/or to yield values of [η] th...

We study the entanglement properties of polyelectrolytes in salt-free and excess salt solution, corresponding to rod-like and expanded coil conformations respectively. While the solvent's ionic strength has a large impact on the conformation of polyelectrolytes, it does not affect its entangle-ment properties. This contradicts current models and su...

The zero-shear rate of non-entangled sodium polystyrene sulfonate in salt-free aqueous solution is evaluated as a function of polymer concentration (c) and degree of polymerisation (N). The range of validity of different empirical equations is established as a function of molar mass and polymer concentration. Deviations from the scaling prediction...

Divalent counterions promote attractive forces between polyelectrolyte chains via electrostatic bridging, which play an important role in the conformation of ionic biopolymers. Further, counterion valence is known to affect the flexibility and aggregation properties of polyelectrolytes in solution. The present study seeks to resolve the effect of c...

Viscosity data for aqueous solutions of sodium carboxymethyl cellulose as a function of polymer concentration (c), added salt concentration (cS) and degree of polymerisation (N) are presented. In dilute solution, NaCMC adopts an expanded coil conformation in excess salt (R ∝ N0.59, [η] ∼ N0.786) and a rod-like conformation (R ∝ N, [η] ∼ N2) in salt...

Thermoresponsive polymeric gels are a class of smart materials with the ability to absorb or release large amounts of solvent when changes in their environment occur. Scaling theories of gel swelling (de Gennes' c * theorem and Obukhov's model) predict that the swelling of a gel correlates with that of a linear chain with equal degree of polymerisa...

Sodium polyacrylate (NaPA) in dilute aqueous solution at an ionic strength of [NaNO3] = 0.01 M establishes a rich phase behaviour in the presence of low amounts of silver cations, which were introduced at a few millimoles or less by replacing the corresponding amount of Na+ cations. Beyond an extremely low level of Ag+ cations, anionic PA chains ag...

Intermediate filaments are a major structural element in the cytoskeleton of animal cells that mechanically integrate other cytoskeletal components and absorb externally applied stress. Their role is likely to be linked to their complex molecular architecture which is the product of a multi-step assembly pathway. Intermediate filaments form tetrame...

Divalent counterions promote attractive forces between polyelectrolyte chains via electrostatic bridging, which play a significant role in the conformation of ionic polymers. Further, counterion valency is known to affect the flexibility and aggregation properties of polyelectrolytes in solution. The present study seeks to resolve the effect of cou...

Reported is an unanticipated mechanism of attractive electrostatic interactions of fully neutralized polyacrylic acid (PAA) with like‐charged surfactants. Amphiphilic polymer‐surfactant complexes with high interfacial activity and a solubilization capacity exceeding that of conventional micelles are formed by bridging with Ca2+ ions. Incorporation...

We present steady shear rheology data for sodium polystyrene sulfonate (NaPSS) in semidilute unentangled salt-free aqueous solution as a function of polymer concentration (c) and degree of polymerisation (N). The measured terminal modulus (G) agrees with the scaling prediction of G ≈ k_BTc/N. The specific viscosity varies with degree of polymerisat...

We report an unanticipated mechanism of electrostatic attractive interactions of fully neutralized polyacrylic acid (PAA) with like‐charged surfactants. Amphiphilic polymer‐surfactant complexes with high interfacial activity and solubilisation capacity exceeding that of conventional micelles are formed via bridging with Ca2+ ions. Incorporation of...

We report an unanticipated mechanism of electrostatic attractive interactions of fully neutralized polyacrylic acid (PAA) with like‐charged surfactants. Amphiphilic polymer‐surfactant complexes with high interfacial activity and solubilisation capacity exceeding that of conventional micelles are formed via bridging with Ca2+ ions. Incorporation of...

We report dynamic light scattering data for a PNIPAM based microgel copolymerised with 2% ionic co-monomers. The hydrodynamic radius is measured as a function of temperature (which varies the solvent quality) and added salt concentration (c_S) from salt-free conditions up to c_S = 0.1 M. Incorporation of the ionic co-monomer leads to an increase of...

We comparatively examine materials and approaches for the fabrication of microfluidic devices for small angle neutron scattering (SANS). Representative inorganic glasses, metals, and polymers are evaluated under typical SANS configurations. Performance criteria include neutron absorption, scattering background and activation, as well as spatial res...

The rheology of water-soluble polyelectrolytes at intermediate and high concentrations is controlled by entanglement, hydrophobic, and electrostatic interactions, whose influences are difficult to isolate. We investigate the rheology of semidilute solutions of sodium carboxymethyl cellulose (NaCMC) with molecular weight Mw ≃ 2.5 × 105 g/mol and var...

We present steady shear rheology data for sodium polystyrene sulfonate (NaPSS) in semidilute unentangled salt-free aqueous solution as a function of polymer concentration (c) and degree of polymerisation (N). The measured terminal modulus (G) agrees with the scaling prediction of G = kBTc/N. The specific viscosity varies with degree of polymerisati...

Thermoresponsive polymeric gels are a class of smart materials with the ability to absorb or release large amounts of solvent when changes in their environment occur. Gel swelling scaling theories (de Gennes c* theorem and Obukhov's model) predict that the swelling of a gel correlates with that of a linear chain with equal degree of polymerisation...

The rheology of water soluble polyelectrolytes at intermediate and high concentrations is controlled by entanglements, hydrophobic and electrostatic interactions , whose influences are difficult to isolate. We investigate the rheology of semidilute solutions of sodium carboxymethyl cellulose (NaCMC) with molecular weight M w ≈ 2.5 × 10 5 g/mol and...

The coupling of droplet microfluidics and Small Angle Neutron Scattering (SANS) is demonstrated with a range of model systems: isotopic solvent (H2O/D2O) mixtures, surfactant (sodium dodecyl sulfate, SDS) solutions and colloidal (silica) suspensions. Several droplet carrier phases are evaluated and fluorinated oil emerges as a suitable fluid with m...

div> We report an analytical approach to study the kinetics of desorption and exhaustion of a hydrophobic dye in a multicomponent washing model environment. The process of dye transfer between an acceptor textile (white polyamide), detergent micelles and a donor textile (red polyester) was quantified by a combination of colorimetric analyses. UV-...

The swelling of thermoresponsive microgels is widely modelled through Flory-Rehner theory, which combines Flory-Huggins solution thermodynamics with the affine network model of elasticity. While it has been shown that FR theory closely follows experimental results for a range of systems, the large number of free parameters required to fit size vs....

The rheology of water soluble polymers at intermediate and high concentrations is controlled by entanglements, hydrophobic and electrostatic interactions. It is often difficult to separate their influence. We report rheology data for solutions of sodium carboxymethyl cellulose (NaCMC) with varying degree of substitution (D.S.) and molar mass as a f...

Vimentin intermediate filaments (IFs) are part of a family of proteins that constitute one of the three filament systems in the cytoskeleton, a major contributor to cell mechanics. One property that distinguishes IFs from the other cytoskeletal filament types, actin filaments and microtubules, is their highly hierarchical assembly pathway, where a...

We report a microfluidic approach to perform small angle neutron scattering (SANS) measurements of contrast variation and matching, extensively employed in soft and biological matter research. We integrate a low scattering background microfluidic mixer and serpentine channel in a SANS beamline to yield a single phase, continuous flow, reconfigurabl...

We investigate the conformation and rheology of sodium car- boxymethyl cellulose (NaCMC) solutions. Scaling laws for the overlap and entanglement concentrations are established in salt free, NaCl and NaOH solutions. NaCl screens electrostatic interactions but not hydrophobic ones, while NaOH screens both. In salt free and NaCl solution, a highly su...

We investigate the viscosity dependence on concentration and molecular weight of semiflexible polyelectrolyte sodium carboxymethylcellulose (NaCMC) in aqueous salt-free and NaCl solutions. Combining new measurements and extensive literature data, we establish relevant power laws and crossovers over a wide range of degree of polymerization (N) as we...