Nonsolvent Solvent Research Articles

Impact of Nonsolvent–Solvent Affinity on Membrane Morphology and Microstructure: Unraveling the Transition from Traversing Pore to Closed Void Structures

Impact of Nonsolvent–Solvent Affinity on Membrane Morphology and Microstructure: Unraveling the Transition from Traversing Pore to Closed Void Structures

Controlling Cellulose Membrane Performance via Solvent Choice during Precursor Membrane Formation

Fabrication of cellulose membranes by alkaline hydrolysis of cellulose acetate (CA) membranes is a simple alternative method to preparing cellulose membranes via phase inversion from their ionic liquid solutions. In this study, three different solvent systems were used to fabricate cellulose acetate membranes by phase inversion, which are dimethyl sulfoxide and its mixtures with acetone and acetic acid. Acetone as cosolvent led to an asymmetric morphology with the densest selective layer, whereas acetic acid led to a loose, almost isotropic structure with high porosity and pore connectivity, also reflected in the pure water permeance and molecular weight cutoff (MWCO) of the CA membranes. Comparing the effects of these cosolvents on the phase inversion process, acetic acid decreased the solvent quality, increased nonsolvent–solvent interactions, and in total decreased the polymer solutions’ stability against phase separation. The phase inversion rate when acetic acid was used as cosolvent was also markedly lower, which was attributed primarily to the solvent’s much higher viscosity. After alkaline hydrolysis of the CA membranes, which converted them into cellulose membranes, the permeance and MWCO of large-pore, small-pore, and dense membranes changed in different directions. This was attributed to a changing membrane structure due to partial degradation of cellulose chains in an alkaline medium, which in turn can affect transport through both the pores and the membrane matrix.

Delayed Solvent-Nonsolvent Demixing Preparation and Performance of a Highly Permeable Polyethersulfone Ultrafiltration Membrane.

Membrane performance optimization is a critical preparation step that ensures optimum separation and fouling resistance. Several studies have employed additives such as carbon and inorganic nanomaterials to optimize membrane performance. These particles provide excellent results but are rather costly, unstable and toxic to several biological organs. This study demonstrated that performance enhancement can also be achieved through delayed solvent-nonsolvent demixing during phase inversion membrane preparation. The rate of solvent-nonsolvent demixing was delayed by increasing the concentration of the solvent in the coagulation bath. This study employed synthetic and real water samples and several analytical techniques to compare optimized performances and properties of membranes prepared in this study with that of nanoparticle-embedded membranes in the literature. Pure water flux and BSA rejection of the membranes prepared in this study were comparable to those of nanoparticle embedded membranes. This study also shows the influence of delayed solvent-nonsolvent demixing on membrane properties such as morphology, wettability, surface roughness and porosity, thereby showing the suitability of the technique in membrane optimization. Furthermore, fouling studies showed that membranes prepared in this study have high flux recovery when fouled by humic acid feed water (>95%) and above 50% flux recovery with real water samples.

Self-Organized Wrinkling in Thin Polymer Films under Solvent–Nonsolvent Solutions: Patterning Strategy for Microfluidic Applications

Self-organized wrinkling instabilities in thin polymer films have instigated a field of versatile surface patterning and have spurred several research efforts in developing micro- and nanopatterned templates for a wide range of applications. Here, we report for the first time a distinct class of wrinkles in a thin polymer (polystyrene, PS) film coated on a substrate under a mixture of organic solvent and aqueous nonsolvent. The solvent (dimethyl formamide, DMF) softens and swells the polymer and paves the way for wetting of the hydrophilic substrate (≥46 mJ/m2) by the solvent–nonsolvent (S-NS) mixture, leading to wrinkle formation. It is investigated that selective delamination-induced wrinkling is a generic phenomenon and takes place in various polymers as well as different combinations of solvent–nonsolvent mixtures. The surface energy of the substrate and the composition of the solvent–nonsolvent mixture play a critical role as wrinkling is not observed on substrates with lower surface energy (<46 mJ/m2). An isotropically distributed yet disordered self-organized wrinkle network of hollow buried channels is formed, and it is illustrated that these can be exploited to generate a mesh of microwires and harnessed to form highly directional patterns using electron beam lithography, which can turn the new leaf for nano- and microfluidic device fabrication platforms.

Structure and Properties of Polyethersulfone Membranes Based on Polyethersulfone–Nonsolvent–Solvent Systems

The effect of degree of saturation of casting solutions (α*—the ratio of the nonsolvent amount added to the polymer solution to the non-solvent amount which causes phase separation) and nonsolvent power on the structure and performance of membranes prepared from system “Polyethersulfone (PES)– non-solvent–solvent” have been studied. Nonsolvent power has been characterized in terms of precipitation number (PN), i.e., the amount of nonsolvent that leads to phase separation of 100 mL of a 1% PES solution. Glycerol (PN = 27.8 g/dL), polyethylene glycol 400 (PN > 1000 g/dL), and their mixtures have been used as a nonsolvent additive to the casting solution. It has been shown that membranes with a nice spongy structure are formed in the case of using casting solutions located near the binodal line. In this case, the membrane flux depends on the nonsolvent power: the higher the PN of the nonsolvent, the higher the membrane flux. The highest flux is exhibited by membranes prepared from casting solutions with a degree of saturation of α* = 0.52–0.81 depending on the PN of the nonsolvent. In this case, macrovoids are present in the structure of the supporting layer of the membranes; the size and shape of the macrovoids also depend on the PN of the nonsolvent: the higher the PN, the larger the macrovoid size in the membrane supporting layer. The results have made it possible to propose a new approach to obtaining PES membranes with a desired structure and properties.

On the thermal performance of a novel PCM nanocapsule: The effect of core/shell

To control the particle size distribution of nanocapsules, the nanoencapsulation of paraffin wax with polyurethane (PU) is performed via the interfacial polymerization. For this purpose, the spherical and solid nanoparticles of paraffin wax are first prepared using the novel semi solvent-non solvent method in the presence of sodium dodecyl sulfate (SDS). Then, the obtained nanoparticles are encapsulated with a polyurethane shell, based on novolac and toluene 2,4-diisocyanate (TDI). The chemical structure, thermal performance, microstructure and morphology of nanocapsules are investigated. The FESEM results confirm the formation of spherical paraffin wax nanoparticles with a particle size distribution of 25–185 nm. The effect of core/shell mass ratio on the thermal properties of the obtained nanocapsules was studied. According to DSC results, the energy storage efficiency and the energy storage capacity of adequate nanocapsules are 80.2% and 97.5%, respectively. The successful nanoencapsulation of paraffin wax with a polyurethane-based shell is confirmed by TEM analysis. Moreover, the thermal cycling tests indicate the high thermal resistance of prepared core-shell system, even after 100 heating/cooling cycles, and have an excellent potential for energy storage and release performance of the system.

Functionalized PCL/HA nanocomposites as microporous membranes for bone regeneration.

In the present work, microporous membranes based on poly(ε-caprolactone) (PCL) and PCL functionalized with amine (PCL-DMAEA) or anhydride groups (PCL-MAGMA) were realized by solvent-non solvent phase inversion and proposed for use in Guided Tissue Regeneration (GTR). Nanowhiskers of hydroxyapatite (HA) were also incorporated in the polymer matrix to realize nanocomposite membranes. Scanning Electron Microscopy (SEM) showed improved interfacial adhesion with HA for functionalized polymers, and highlighted substantial differences in the porosity. A relationship between the developed porous structure of the membrane and the chemical nature of grafted groups was proposed. Compared to virgin PCL, hydrophilicity increases for functionalized PCL, while the addition of HA influences significantly the hydrophilic characteristics only in the case of virgin polymer. A significant increase of in vitro degradation rate was found for PCL-MAGMA based membranes, and at lower extent of PCL-DMAEA membranes. The novel materials were investigated regarding their potential as support for cell growth in bone repair using multipotent mesenchymal stromal cells (MSC) as a model. MSC plated onto the various membranes were analyzed in terms of adhesion, proliferation and osteogenic capacity that resulted to be related to chemical as well as porous structure. In particular, PCL-DMAEA and the relative nanocomposite membranes are the most promising in terms of cell-biomaterial interactions.

Process intensification approach for preparation of curcumin nanoparticles via solvent–nonsolvent nanoprecipitation using spinning disc reactor

Continuous preparation of curcumin nanoparticles via solvent–nonsolvent (S-NS) precipitation by using spinning disc reactor was investigated. The process intensification by spinning disc reactor (SDR) along with the comparative study of conventional mechanical agitated contactor was carried out. Solvent used for curcumin precipitation in this study was ethanol whereas non-solvent deionised water. Influences of various operating parameters for spinning disc process; such as flow rate of S-NS, S-NS ratio, concentration of curcumin, disc characteristics, concentration of protecting agent and rotating disc speed were examined on the nanoparticles size. The average optimum curcumin particles size was obtained in the range 180–220nm in consideration with particles size distribution at a flow rate of 200mLmin−1; curcumin concentration of 0.5gL−1 in ethanol; polyvinylpyrilodine (PVP) concentration of 1gL−1 in deionised water; S:NS ratio 1:4 and operating disc speed of 1500rpm. Particles were characterized by using XRD, FT-IR, DSC and SEM which showed decrease in the crystallinity after the nanoprecipitation of curcumin. The dissolution rates of the fabricated curcumin nanoparticle were found drastically higher than original curcumin.

Cross-linked hyaluronic acid sub-micron particles: in vitro and in vivo biodistribution study in cancer xenograft model

This paper focused on the biodistribution of the cross-linked hyaluronic acid (HA-NPs) sub-micron particles in tumor-bearing mice. Solvent-non solvent method followed glutaraldehyde cross-linking utilized for the fabrication of HA-NPs. Size measurement and morphological analysis were performed by dynamic light scattering and electron microscopy, respectively and the size found to be in the range of 200-400nm. In vitro viability in LNCaP cell line was assessed by water soluble tetrazolium assay after 24h of exposure to sub-micron particles and no toxicity was found to higher concentration of 3mg/mL. Internalization of particles in prostate cancer cell LNCaP were studied by confocal microscopy with FITC labeled submicron particles and involvement of hyaluronan receptor mediated uptake/endocytosis was confirmed by competitive assay. Biodistribution studies were performed in xenograft prostate cancer mice model with fluorophore labeled particles and monitored in tumoral parenchyma with strong fluorescence, meanwhile very less signal in liver, kidney and spleen while no fluorescence found in lung after 24h of systemic administration; that shown ability of this HA based system to recognize cancer tissue. These result fetched that hyaluronic acid based system is selective for tumoral site and can be utilized to deliver bioactives in specific (targeting) and controlled (temporal) manner to cancerous tissue.

The effect of surfactants on the structure and performance of PES membrane for separation of carbon dioxide from methane

In the present study, the effects of three types of surfactants including sodium dodecyl sulphate (SDS), cetyle three methyl ammonium bromide (CTAB), and Triton X-100 on structure and performance of polyethersulfone membranes for carbon dioxide separation from methane were investigated. Flat sheet gas separation membranes of polyethersulfone (PES) and its mixture with different concentration of surfactants in casting solution were fabricated through a dry/wet induced phase inversion process. Ternary phase diagrams of polymer–solvent–nonsolvent for pure PES and its mixture with surfactants were drawn using titration method. Investigation of crystal phase compositions of the prepared membranes were carried out by X-ray diffraction analysis and measuring glass transition temperatures. Scanning electron microscopy (SEM) was used to study the effect of surfactant type and surfactant concentration on the morphology of membranes. Also, to understand the intermolecular interactions, the membranes were characterized by Fourier Transform Infrared (FTIR) spectroscopy. Separation performances of the membranes were evaluated using pure CH4, CO2, N2 and binary CO2/CH4 mixed gas permeance measurement. The results indicate that addition of surfactants in the casting solution increases the membrane porosity and membrane gas permeance and decreases CO2/CH4 ideal selectivity, except for Triton X-100 which increases CO2/CH4 selectivity. The effects of feed pressure, feed temperature and feed composition on the membrane performance were investigated through mixed gas experiments.

Preparation of highly porous β-chitin structure through nonsolvent–solvent exchange-induced phase separation and supercritical CO2 drying

A highly open, porous, three-dimensional β-chitin network structure with meso- and macropores was successfully fabricated by exploiting nonsolvent–solvent exchange-induced phase separation and supercritical CO2 drying processes. It was revealed that a formation of the highly porous structure, consisting of interconnected micro-scale mesoporous chitin particles and nano-scale fibrils, was favored by repeating the freeze–thaw cycle of the chitin–formic acid solution. The sodium hydroxide (NaOH) solution was used to remove the residual formic acid in the chitin gel network during the neutralization step. Nitrogen adsorption was used to characterize the properties of the mesopores, which were found to be in the range of 5–25 nm. The crystalline structure was also investigated by X-ray diffraction, which revealed a conversion of β-chitin to α-chitin during the fabrication and drying processes.

PREPARATION AND CELL AFFINITY EVALUATION OF POLYLACTIDE FILM WITH MICRO-PATTERNED SURFACE

The polylactide(PLA) and polystyrene(PS) films with micro-patterned surfaces were prepared via solvent-non-solvent(SNS) method and mold method.Based on these prepared micro-patterned PLA films,the effect of surface structure on the wettability was evaluated by water contact angle measurement,and the cell’s behaviors(including adhesion and proliferation) on PLA film were further discussed by scanning elctron microscopy(SEM) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide(MTT) assay in this study.The results showed that a dense regular micro-pits structure with about 20 μm diameter could be got on the surface of PLA and PS films under semi-closed condition,and 1 μm under vacuum condition by SNS method.Using micro-pits patterned PS films as mold,the PLA films with about 20 μm and 1 μm micro-islands patterned surfaces could be achieved.The surface hydrophobicity of PLA films was enhanced because of the micro-patterned surface(water contact angle 90°).Osteoblast showed a better spread on the patterned surface and the amount of cells was higher than that on the smooth surface,but the cell growth curve was gently on the patterned surface,indicating that the micro-patterned surface benefited cell’s adhesion,but contributed little for improving cell’s proliferation.

Effect of solvents on performance of polyethersulfone ultrafiltration membranes: Investigation of metal ion separations

The new polyethersulfone (PES) based ultrafiltration membranes were formed using a two stage process of dry and wet phase inversion in non solvent coagulation bath. The effects of three different solvents such as, N, N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP) and Dimethyl sulphoxide (DMSO) of 82.5% and 85% concentrations on the performance of final membranes were extensively investigated. Scanning electron microscopy (SEM) image results proved that PES membranes with an asymmetric structure were successfully formed. The number of pores formed on the top layer of PES membranes using above-mentioned three solvents was the result of the combined effect of the thermodynamic properties of the system (composition, concentrations, and phase behaviour) and membrane formation kinetics, whereas, the formation of the macroporous sub layer of those membranes was controlled by the diffusion rate of solvent–nonsolvent. The flux of pure water, membrane resistance, mechanical stability, molecular weight cut-off (MWCO) and separation performance of the PES membranes were studied. Separation of metal ions from aqueous solutions was studied for Ni(II), Cu(II) and Cr(III) using two complexing polymer ligands: polyvinyl alcohol (PVA) and poly(diallyldimethylammonium chloride) (PDDA).The separation and permeate rate (flux) efficiencies of the new membranes are compared using different solvents and different PES/solvent compositions.

Effect of Solvent–Nonsolvent Miscibility on Morphology and Electrochemical Performance of SiO2/PVdF‐HFP‐Based Composite Separator Membranes for Safer Lithium‐Ion Batteries

AbstractAs a new approach to improve the thermal stability of separator membranes crucially affecting the internal short‐circuit failures of lithium‐ion batteries, we develop a new composite separator membrane. The composite separator membrane is prepared by introducing microporous composite coating layers onto both sides of a polyethylene (PE) separator membrane. The composite coating layers consist of silica (SiO2) nanoparticles and gel‐type polymer electrolytes (PVdF‐HFP, polyvinylidene fluoride‐hexafluoropropylene). The microporous morphology of composite coating layers is determined by controlling the phase inversion, more specifically the solvent–nonsolvent miscibility in the coating solutions. To induce the phase inversion, three different nonsolvents are chosen in the decreasing order of solubility parameter (δ) difference against the solvent (acetone, δ = 20 MPa1/2); the non‐solvents are water (δ = 48 MPa1/2), ethanol (δ = 26 MPa1/2), and isopropyl alcohol (δ = 24 MPa1/2). The microporous structure of composite coating layers becomes more developed with the increase of not only the nonsolvent content, but also the solubility parameter difference between acetone and the nonsolvent. Based on this understanding of the phase inversion, the influence of the morphological variation on the thermal shrinkage and electrochemical performance of the composite separator membranes is quantitatively identified.magnified image

Structure and gas permeability of asymmetric polyimide membranes made by dry–wet phase inversion: Influence of alcohol as casting solution

AbstractIn this article, we have reported the influence of alcohol as a casting solution on the structure and the gas permeability of asymmetric polyimide membranes made by dry–wet phase inversion. The apparent skin layer thickness of the asymmetric membrane decreased with an increase in molecular weight of the alcohol, and the thicknesses of the membranes made from methanol, ethanol, propanol, and butanol were 250, 120, 61, and 31 nm, respectively. We found that χ12 as an interaction parameter of solvent–nonsolvent had a significant influence on the phase inversion occurring in the coagulant medium. On the other hand, the gas permeance and the gas selectivity in the asymmetric membranes increased with the increasing molecular weight of the alcohol. We believe that a more packed structure formed in the asymmetric polyimide membrane with a thinner surface skin layer is also responsible for the thickness‐dependence of the gas selectivity obtained in this study. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2739–2746, 2007

Phase behavior of poly( N-isopropylacrylamide) in water–methanol cononsolvent mixtures and its relevance to membrane formation

The phase behavior of poly ( N-isopropylacrylamide) (PNIPAAm) in solutions composed of water and methanol was studied at 25 °C. The pair of solvents used to dissolve PNIPAAm has been selected for the purpose to perform a cononsolvent system. From the observed phase behavior, PNIPAAm was soluble in either water or methanol individually but liquid–liquid demixing was observed in water/methanol mixtures. Flory–Huggins formalism including three binary interaction parameters and one ternary interaction parameter was used to analyze the phase behavior of the cononsolvent system. The mechanism of cononsolvency and its relation with the ternary interaction parameter were discussed. In addition, the use of two solvents serving as a cononsolvent system, replacing the traditional solvent–nonsolvent pair, for the membrane formation was investigated. Regardless of water or methanol being used as the solvent, it showed a rapidly precipitating system and macrovoid morphology due to liquid–liquid demixing was obtained. Trend expected on the basis of the phase diagram was in reasonable agreement with the observed membrane morphology. Therefore, the principles of membrane formation established for the ternary systems with nonsolvent–solvent–polymer can be extended to a cononsolvent–polymer system.

Polyetherimide membrane formation by the cononsolvent system and its biocompatibility of MG63 cell line

Polyetherimide (PEI) membrane could be prepared by immersion–precipitation process by using the N-methyl-2-pyrrolidone (NMP)–methylene chloride (MC) cononsolvent as the coagulation medium. The membrane, via scanning electron microscopy (SEM), showed a typically asymmetrical structure consisting of a thin and dense skin layer, sponge morphology in the cross-section and porous bottom surface. Trend expected on the basis of the phase diagram of the use of two solvents serving as a cononsolvent system for the membrane formation, replacing the traditional solvent–nonsolvent pair, was in reasonable agreement with the observed membrane morphology. Therefore, the principles of membrane formation established for the ternary systems with polymer–solvent–nonsolvent can be applied to a polymer–cononsolvent (solvent–solvent) system. Furthermore, the biocompatibility of the PEI membrane top (dense) and bottom (porous) surfaces was assessed in an in vitro model using the human osteoblast-like cell line MG63. Compared to cells grown on tissue culture polystyrene (TCPS), cells cultured on the PEI membranes had lower cell growth, but every single cell on the PEI membrane showed similar viability to control cells. SEM analysis showed comparable adhesion and confluence characteristics on all substrates. In addition, the levels of alkaline phosphotase (ALP), prostaglandin E2 (PGE 2) and transforming growth factor β1 (TGF-β1) cytokines produced by MG63 cells on the prepared PEI membranes, regardless of the top or bottom surface, were similar to those on TCPS. The results of this study suggest that the PEI membrane prepared from a cononsolvent system is a non-toxic, biocompatible substrate for the proliferation of human bone cells in vitro.

Preparation and hydrophilicity study of poly(vinyl butyral)-based ultrafiltration membranes

Poly(vinyl butyral) (PVB)-based ultrafiltration membranes were prepared by immersion–precipitation in water coagulation bath. The effects of different factors, such as PVB concentration, scraper clearance, water temperature and especially solvent nature on the performance of final membranes were extensively investigated. The toplayer formation mechanism of the PVB membranes prepared in four different PVB–solvent–water systems was discussed. By comparison with poly(ether sulfone) (PES), the hydrophilicity of PVB was also studied. Experimental results showed that PVB-based ultrafiltration membranes with an asymmetric structure were successfully prepared by the observations of scanning electron microscope (SEM). The formation of the toplayer of the PVB membranes above-mentioned from different solvents was the result of the combination of the equilibrium thermodynamics and membrane formation kinetics, whereas, the sublayer of those membranes was dominated by the diffusion rate of solvent–nonsolvent. The permeability and separation performance of the final PVB membranes could be adjusted under different preparation conditions. PVB–PES blends were the nonmiscible systems, and the increase in mass ratio of PVB in the components decreased the surface contact angle of the resulting PVB–PES composite membranes from 81.0° to 76.6°. In phase diagram, the width of the liquid–liquid homogeneous region of the PES–DMAC–water system was very close to but slightly smaller than that of the PVB–DMAC–water system, which indicated that PVB was a little more hydrophilic than PES while in solution.

Surface Modification of Amberlite XAD‐4 Resin with D2EHPA by a Two‐Step, Solvent–Nonsolvent Procedure and the Application on the Selective Separation of Lead and Copper Ions

Di(2‐ethylhexyl)phosphoric acid (D2EHPA) has the tendency to adsorb at interfaces in an oriented fashion due to the amphiphilic structure. The study of the surface tension shows that the adsorption of D2EHPA at interface can lower the surface tension of ethanol solution. The amount of adsorption is affected by the pH and ionic strength of the solution. Being a small surface‐active molecule, a monolayer of D2EHPA molecules can be immobilized on the surface of nonpolar Amberlite XAD‐4 resin by a two‐step, organic solvent–nonorganic solvent process. The amount of immobilized D2EHPA is as high as 1.02 (mol/kg of resin). The electron spectroscopy for chemical analysis (ESCA) results show that the immobilized D2EHPA undergoes reorientation by further exposing the phosphoric acid group to the water phase. Since the hydrophobic alkyl chains of D2EHPA physically entangle with the surface polymer chains of Amberlite XAD‐4, the immobilized extractant has good stability on the resin surface. This D2EHPA‐modified Amberlite XAD‐4 can be used for the separation of lead and copper ions as an ion‐exchange resin. Ion‐exchange isotherm experiments show that D2EHPA‐modified resin has higher Pb ion affinity than Cu ion. This new type of D2EHPA‐modified resin shows better Pb and Cu ions separation than analogous D2EHPA‐impregnated resin [extractant‐impregnated resin (EIR)] and solvent extraction system. The selective separation results using series contacts of solution mixtures with resins further demonstrated the feasibility of using D2EHPA‐modified Amberlite XAD‐4 resin for the separation of Pb/Cu mixed ion solution. After only six batches of contacts, the relative ion concentration of Cu ion increases from 50% to more than 99%, while the relative ion concentration of Pb ion decreases from 50% to less than 1%. The Cu recovery rate is more than 75%, comparing to 54% in the EIR system.

Molar mass effects in reversed-phase gradient polymer-elution chromatography of oligomers

The dependence on molar mass of the retention of oligomers in reversed-phase gradient polymer-elution chromatography (RP GPEC) has been investigated. To this end a variety of oligomer series, including polystyrene (PS) and amorphous polyesters (PE) were chromatographed using different non-solvent-solvent (NS-S) mobile phases and at different temperatures. Sigmoidally shaped curves were usually obtained for plots of amount (%) of S against 1/√ (molar mass) but the exact shape varied from almost linear to very convex. Increasing the temperature led to increased dependence of retention on the molar mass; this can be ascribed to a decrease in Flory-Huggins interaction parameters. Changing the NS-S system substantially affects the shape of the curves, but the effect is different for different oligomer series. From results from isocratic measurements for PS and a PE it was found that the effect of experimental conditions can be ascribed to the relative contributions to retention of both end groups and of the monomer repeat units. Because these contributions are affected to different extents by chromatographic conditions, changing these conditions also affects the shape of the plot of the amount of S against 1/√ (molar mass).