The proposed model combines simple Boltzmann sigmoidal and 1 - exp expressions. The obtained kinetics parameters were proven to be useful to discriminate the effects of incubation variables and also to perform enzyme screening.
Furthermore, it is proposed that the energy dissipation of a film subject to enzymatic hydrolysis brings to light its structural changes. Overall, it is demonstrated that the variations registered in QCM frequency and dissipation of the film are indicative of mass and morphological transformations due to enzyme activities; these include binding phenomena, progressive degradation of the cellulose film, existence of residual, recalcitrant cellulose fragments, and the occurrence of other less apparent changes throughout the course of incubation.
Publication Date: Publication Name: Langmuir. Polymer adsorption. BC nanoribbons were produced by a BC nanoribbons were produced by a Colombian native strain of Gluconacetobacter medellinensis; the nanocomposite was plasticized with glycerol and crosslinked with citric acid. The reinforcement percentage in the nanocomposites remained constant throughout the fermentation time because of the TPS absorption capability of the BC network.
Nanocomposites produced after fermentation for seven days were characterized using thermogravimetric analysis TGA ; Fourier transformed infrared spectroscopy with attenuated total reflectance FTIR-ATR , mechanical testing and scanning electron microscopy SEM. These findings support the applications of starch in the packaging industry. Ultrathin film coatings of aligned cellulose nanocrystals from a convective-shear assembly system and their surface mechanical properties more.
On the interactions between cellulolytic enzymes with native, autohydrolysis and technical lignins and the effect of a polysorbate amphiphile in reducing non-productive binding more. Understanding enzyme-substrate interactions is critical in designing strategies for bioconversion of lignocellulosic biomass.
In this study we monitored molecular events, in-situ and in real time, including the adsorption and desorption In this study we monitored molecular events, in-situ and in real time, including the adsorption and desorption of cellulolytic enzymes on lignin and cellulose by using quartz crystal microgravimetry and surface plasmon resonance. The effect of a non-ionic surface active molecule was also elucidated. The results indicated a high affinity between the lignins with both, monocomponent and multicomponent enzymes.
More importantly, the addition of non-ionic surfactants at concentrations above their critical micelle concentration reduce This latter, remarkable behavior was ascribed to coupled water expulsion from the interface upon charge neutralization of anionic surface sites with adsorbing cationic polymer segments. Finally, random copolymers with similar composition adsorbed to a larger extent compared to the respective block copolymers, revealing the effect of adsorbed loops and tails as well as hydration.
The role of polyampholyte charge density on its interactions with cellulose more. SUMMARY: Polyampholytes offer considerable promise as dry-strength additives, but the molecular mechanism involved in their adsorption needs to be better understood. Amphoteric terpolymers of acrylamide, itaconic acid, and The basic groups ranged from 2. Publication Date: Nanoindenter-based scratch nanoscratch tests were successfully used to study lubrication at the microscale in the presence of a fluid film.
The influence of aqueous lubricants on both hydrophobic polypropylene and polyethylene and The influence of aqueous lubricants on both hydrophobic polypropylene and polyethylene and hydrophilic cellulose surfaces was investigated.
The lubricants consisted of aqueous solutions of amphiphilic block copolymers of ethylene oxide EO and propylene oxide PO. The coefficients of friction were measured in the presence of lubricant solution on the solid surfaces. An improved lubricity i. In—situ Glyoxalization during Biosynthesis of Bacterial Cellulose more.
Effect of charge balance and dosage of polyelectrolyte complexes on the shear resistance of mineral floc strength and reversibility more. We evaluated the effect of polyelectrolyte complexes PEC with varying balance of charges on the flocculation of precipitated calcium carbonate PCC particles.
Light transmission was used in real time to monitor the dynamics of flocculation under shear fields. Compared to the single polyelectrolytes, PECs greatly enhanced particle re-flocculation while minor differences in shear resistance were observed. Shear resistance and re-flocculation depended strongly on the molecular weight and charge ratio of the PEC components. In order to achieve floc stability and re-flocculation conditions a minimum concentration of charge-asymmetric PEC should be applied.
Hydrophobic particles based on dodecyl 3,4,5-trihydroxybenzoate LG were coupled onto the surface of cellulose nanofibrils CNFs and silica by treatment with a multicomponent colloidal system MCS derived from the laccase-mediated Hydrophobic particles based on dodecyl 3,4,5-trihydroxybenzoate LG were coupled onto the surface of cellulose nanofibrils CNFs and silica by treatment with a multicomponent colloidal system MCS derived from the laccase-mediated reaction of LG in the presence of a sulfonated lignin SL.
The colloidal stability of MCS and its components in water was followed by measuring space- and time-resolved light transmission and back scattering. It also facilitated the surface enzymatic reaction that led to adsorption and coupling of MCS onto CNFs and silica surfaces. Surface pretreatment with chitosan further increased the extent of MCS adsorption on the surfaces. This method represents a sustainable alternative to traditional approaches for cellulose hydrophobization and a step forward in implementing green routes for surface modification.
Development and characterization of thin polymer films relevant to fiber processing more. The addition of CNF to the aqueous phase expanded the CNF also increased the viscosity of the continuous phase and reduced the drop size both of which increased the stability and effective viscosity of the emulsions. Overall, CNF are a feasible alternative to conventional polysaccharides as stability enhancers for normal and multiple emulsions that exhibit strong shear thinning behavior.
Microcrystalline Cellulose. Formation and application of functional coatings on synthetic fibers more. We present two simple methods for modifying synthetic fibers made of polypropylene PP and poly ethylene terephthalate PET. Specifically, we alter the inert PP fiber mats by physisorbing denatured proteins, and cross-linking the Specifically, we alter the inert PP fiber mats by physisorbing denatured proteins, and cross-linking the protein layers using glutaraldehyde.
The amino- and hydroxyl-functionalities present in the protein coatings serve as attachment points for polymerization initiators. In addition, PET fibers are modified chemically by amidation with 3-aminopropyltriethoxysilane APTES , followed by hydrolysis, which yields silanol groups that permit surface attachment of the initiator molecules. Selected applications of these functional fibers will be outlined b Protein adsorption , Polypropylene , and Poly Ethylene Terephthalate.
Ethylcyanoacrylate fixation of the cranial bone flap after craniotomy more. This procedure was done in order to evaluate the efficacy and safety of ethylcyanoacrylate as an adhesive for fixation of the bone flap. One hundred consecutive craniotomies in patients older than 16 years in which the bone flap was fixed One hundred consecutive craniotomies in patients older than 16 years in which the bone flap was fixed with ethylcyanoacrylate were studied.
The osteosynthesis and any complications in all cases were followed clinically and radiologically for 3 months. This technique proved to be safe, fast, and easy to accomplish, with immediate stability of the bone flap and excellent cosmetic results. Foamability and foam stability at high pressures and temperatures. Instrument validation more. An instrument was designed and assembled with the aim of measuring macroscopic properties of foams such as foamability and stability under high pressures and moderate temperatures up to bar and K, respectively.
The device The device makes use of infrared sensors to detect the foam forefront position as it is generated by gas sparging in the foaming solution. The measurement. Dispersion of cellulose crystallites by nonionic surfactants in a hydrophobic polymer matrix more. Materials Engineering , Chemical Engineering , and polymer science and Engineering.
Short-range interactions between non-ionic surfactant layers more. Short-range interactions between surfactant and lipid layers are of great importance in technical applications in complex fluids such as foams, dispersions and emulsions, as well as in the formulation and performance of dispersants, Short-range interactions between surfactant and lipid layers are of great importance in technical applications in complex fluids such as foams, dispersions and emulsions, as well as in the formulation and performance of dispersants, detergents and flocculants.
It is also of utmost importance in biological systems where interactions between biomembranes influence a range of processes. The field of short-range interactions has been thoroughly investigated during the past 30 years, following the emergence of a number of techniques to measure interaction forces. Bilayer structures with a thickness of about consistently showed the same trend.
We hypothesize that nm are formed 1 h after surfactant addition. The low this effect is due to the polydispersity in the chain length average refractive index of the layer 1.
In fact, the studied corresponding adsorbed amount at this time indicates fluorosurfactant is not monodisperse since in the manu- loosely packed bilayer aggregates. As Later on, when equilibrium is reached, the adsorbed such, we propose that initially at low surfactant con- amount is increased doubled , indicating an increase in centrations longer-chain molecules are preferentially the surface density of the adsorbed bilayer structures.
As the surfactant concentration is increased, that, as demonstrated by the force measurements to be the fluorosurfactant assembled in the adsorbed aggregates presented later , is easy to squeeze away by applying high tends to have a tail length that is closer to the average loads.
The structure of the bilayer surface aggregates is bulk chain length, and therefore the ellipsometric likely to be affected by electrostatic and hydrophobic thickness is reduced. Evidence of such behavior has been interactions. The electrostatic attraction between the presented in the case of adsorbed block copolymers with surfactant cationic groups and the anionic surface provides low polydispersity. The A final general remark on the shape of the adsorption hydrophobic interactions between the fluorosurfactant curve is in place.
Close examination of the adsorption tails promote formation of bilayer aggregates, and the dynamics reveals that after surfactant injection some electrostatic repulsion between the headgroups not in overshooting in the calculated adsorbed amount arises. The detailed structure of different surfactant species at the interface. A more used for elucidation of the adsorption mechanism and the detailed study of this issue is advanced by the interaction possible assembly structure.
As can be seen, the resulting force study. Additional surfactant molecules are incorpo- At low concentration the adsorption of individual rated into the structure. The layer thickness is reduced molecules is driven by electrostatic attraction between to 3 nm, and the refractive index rises up to 1.
This the surfactant and the surface of opposite charge. In this behavior indicates that a more tight packing of the region the surface charge density of the surface varies molecules within the bilayer is attained. A relatively small increase of the adsorbed amount fluorosurfactants, and thus the adsorbed amount increases to a final value of 2.
This change sharply since the process is highly cooperative. The data was accompanied by a marginal reduction of the layer demonstrate that bilayer aggregates start to form in this thickness to 2. It can be envisioned that at a molecular surface charge is neutralized and later reversed by the level the bilayer aggregates pack closer together to the adsorbed surfactant ions.
We note that the index, and layer thickness showed some instability. This adsorbed amount increases marginally, but significantly, can be explained by the effect of thermal and concentration above the cmc.
We suggest that this is a consequence of gradients occurring in the vicinity of the surface which attachment of some surfactant aggregates on top of the produce large changes in the calculated values and bilayer aggregates. This interpretation will be supported formation of fluorosurfactants aggregates in the bulk by the force studies presented below.
At the highest solution that adsorb and desorb from the surface. However, the corre- , , In Anionic Surfactants. Physical Chemistry of in the form of patchy bilayer aggregates. Hence, not even at this concentration is the surface covered by a complete bilayer but rather bilayer aggregates are present.
Following AFM imaging studies, it has been proposed that the dominant structure of single-chain anionic SDS and cationic surfactants CTAB and TTAB adsorbed on mineral oxides surfaces titanium dioxide, kaolinite, and quartz is predominantly spherical or globular surface micelles. Semilogarithmic plot of the interaction force later on strongly indicates the formation of fragmented normalized by radius as a function of surface separation of bilayer assemblies.
The formation of large fluorosurfactant glass spheres across aqueous 0. In both cases no observed in bulk solution66,67 supports the possibility that hysteresis was observed.
In the inset the first curve is shown bilayer-like structures are formed at solid interfaces. This together with a fit to DLVO theory with constant surface charge will be investigated more closely in a coming publication.
In this situation it is possible that additional loose charge extracted from the fitting assuming constant attachment of surfactant assemblies onto the surface surface charge boundary conditions were mV and coated by bilayer aggregates takes place. Surface Interaction Forces. Thus, in the mM NaI background electrolyte are included. As can be surface force studies it is possible to explore not only the seen, there is very little change in the force profile at such effect of adsorption on the interaction forces between the low surfactant concentration.
However, a reduction in the two surfaces but also dynamic phenomena that occur in short-range repulsion is noticed. This change is a conse- the adsorbed surfactant layer s as the interacting surfaces quence of some adsorption of cationic surfactant molecules are moved with respect to each other.
It is possible that We begin discussing a typical MASIF force curve for a an increase in fluorosurfactant adsorption takes place as fluorosurfactant-free solution. Figure 2 shows a semi- the surface separation is reduced.
However, the adsorption logarithmic plot of the interaction force normalized by must by very low since the magnitude of the double-layer radius as a function of surface separation of glass spheres force hardly is affected. Corroboration of this observation across aqueous 0. The force-distance is found in the ellipsometry measurements. On separation relationship for this electrolyte is in excellent agree- no adhesion between the surfaces was observed.
A short time about 2 strength of the solution. At smaller separation, however, h after the fluorosurfactant addition the long-range an additional repulsion is present that supersedes the repulsive double-layer force initially observed disappears expected van der Waals attraction. This short-range due to the neutralization of the surface charge by the repulsive force between glass or silica surfaces in aqueous adsorbed molecules.
As has been discussed before from solutions has been reported previously, and its origin ellipsometric measurements, it is proposed that at this is rationalized in terms of the dehydration of polar silanol concentration surfactant bilayer aggregates adsorb on groups hydration force 71 or to the compression of short the surfaces.
As the surfaces are brought closer, the spatial polysialic acid chains steric repulsion. As the surfaces are at molecular separations, the polar groups of the surfactant face the solid surfaces and the tails face 63 Schulz, J.
Langmuir , 18, Langmuir , 13, It is possible that under this condition 66 Oelschlaeger, C. A , 84, Colloid Interface Such assembly and structural rearrangement promote Sci. Langmuir , a combination of electrostatic attraction between positively 14, Force normalized by radius as a function of surface surfactant solution 0. The equilibration times ca. The curves on separation are not shown, corresponds to the separation outward run after adsorption but in all cases a strong adhesion ca.
On separation an adhesion of about 1. Inset: amplification of the short-range force area. Thus, only the first outermost jump was comparatively short-range attraction between glass sur- observed, i. The measured adhesion is that corresponding in the force curve. Data obtained after more than 10 h of to a bilayer-bilayer contact, which amounts to about 1. Now, a recharging 1.
The lower value of the adhesion between bilayer aggregates compared to the monolayer- force predominates at large separations. At shorter monolayer contact is expected since in this situation separations a van der Waals attraction pulls the surfaces surfactant headgroups rather than tails cover the majority into contact between the bilayer aggregates.
In forces as those typical of monolayer-monolayer contact. At shorter separations a steeply rising force is impossible to force out the surfactants in the outer surface observed. This force originates from dehydration and layer under the experimental loads. In both cases the hard- compression of the bilayer aggregates. At a sufficiently wall contact corresponds to the thickness of a bilayer and high load, about 1.
First, at homogeneous surfactant monolayer coatings e. In this situation reported46 , indicating in the present case low surfactant a strong adhesion is measured. Figure 5. Force normalized by radius as a function of surface Figure 7. All the curves correspond to the approach corresponds to the separation outward run after adsorption or inward runs. The hard-wall or constant compliance zones equilibrium. On separation an adhesion of about 2. Since in the bilayer aggregates the surfactant chains are probably partially intercalated, the actual length of the adsorbed surfactant molecules should be about 1.
A rough calculation using the relationship for the calculation of a surfactant tail length is presented in ref 73; an equivalent hydrocarbon chain for the studied surfactant yields a fully maximum length Lmax of 1. As can be seen, the obtained results fit very well the idea of an adsorbed assembly in the form of a bilayer aggregate. Force normalized by radius as a function of surface showed a layer thickness of 1. The filled black circle curve represents the approach curve for models of a fluorosurfactant similar to the one studied adsorption equilibrium conditions, and the gray circles curve here are reported in refs 75 and 76 for various surface corresponds to the separation outward run after adsorption conformations.
Inset: amplification of the short-range force. In the first case a stronger contact are attainable only the first situation is depicted. Second, the force load required reach bilayer-bilayer contact is also plotted on the positive to achieve bilayer-bilayer contact increases as the sur- side of the graph, and it is evident that an increased load factant concentration is increased.
Above the cmc of the is required as the fluorosurfactant concentration is surfactant 30 ppm , an additional force barrier in excess increased. This is due to a combination of repulsive double- of that crated by electrostatic double-layer forces is observed outside bilayer-bilayer contact.
Third, the distance jump from 73 Evans, D. A similar figure 3. Langmuir , 1, Adhesion forces between glass spheres covered by surfactant assemblies produced after reaching monolayer- monolayer contact open circles or bilayer-bilayer contact filled black circles for different fluorosurfactant concentrations.
These adhesion forces are, as conventionally done, displayed in the negative side of the diagram. The normalized force load required to reach bilayer-bilayer contact gray filled circles Figure 9.
Force normalized by radius of mica surfaces in is also included in the positive side of the plot. M PBS buffer as background electrolyte. The open circle curves correspond aggregates. This common to the cases presented previously. This has also hard wall profile is nm, which is identical to the been observed for e. Therefore, in this case bilayer deposited on mica by LB techniques is much higher.
An aggregates are formed on each surface. In fact, During LB deposition all molecules are initially oriented it has been reported that after the formation of a surfactant with the charged group toward the surface. With time bilayer on mica it becomes impossible to push the two some rearrangements may occur with some molecules in surfaces into strong hydrophobic contact as opposed to the monolayer changing orientation or moving to form an the case of glass surfaces.
In the confined space not straightforward. We for the measured interaction forces. As can be seen, in the also note that vapor cavities form between LB monolayers case of the highest pull-off forces monolayer-monolayer in contact whereas no such cavities were observed in the adhesion , the experimental values do not conform to this present case. For the fluorosurfactants studied here charge neutraliza- tion never occurs at equilibrium.
Clearly, the stronger hydrophobicity of the fluorocarbon chain makes adsorption into monolayer aggregates less favorable since the interfacial tension toward water would be higher.
Instead, we observe that bilayer aggregates form readily once the surface density of adsorbed surfactants has reached a critical level. In contrast, the buildup of bilayer aggregates for CTAB on glass appears to occur more gradually. We note that in both cases bilayer aggregates that are difficult to transform into monolayer aggregates under compression are present on the surfaces at close to half the cmc.
Conclusions Ellipsometric and surface force experiments indicate that cationic fluorosurfactants self-assemble on solid surfaces silica, glass, and mica in the form of bilayer structures. This process takes place at rather low sur- factant concentration and explains the improvement in separation efficiency and peak symmetry reported in the literature when fluorosurfactants are used in capillary electrophoresis.
Adsorption of fluorosurfactants on solid surfaces influ- ences the interaction forces between the adsorbed layers quite dramatically. At low fluorosurfactant concentration the molecules adsorb both on glass and mica surfaces due Figure At higher surfactant fluorosurfactants adsorbed on two approaching surfaces as concentrations hydrophobic interactions continue to drive those in the MASIF or SFA experiments for surfactant the adsorption process.
The situation for large separations and when the surfaces are in contact are illustrated on the left and right side tween LB-deposited monolayers of fluorosurfactants, the of the figure, respectively.
At higher concentrations it is higher, more bilayers aggregates are formed, and mono- difficult impossible to reach monolayer-monolayer layer-monolayer contact is difficult impossible to reach. In this In this situation the measured adhesion corresponds to case the resulting energy of adhesion is an order of bilayer-bilayer contact which, compared to monolayer- magnitude lower than for monolayer-monolayer contact.
It was demonstrated that the structures that start to The structures drawn in the gap for high-concentration build up on solid surfaces at low fluorosurfactant con- conditions represent aggregates of fluorosurfactant mol- centration e. At higher concentration bilayer aggregates between cationic hydrocarbon surfactants and cationic adsorbed on the surface are likely to occur, and molecular fluorocarbon surfactants adsorbing to glass and their effect rearrangement arises as the surfaces come in contact.
Some basic facts are that the electrostatic The force load required to reach bilayer-bilayer contact affinity of the surfactants to the surface is the same increases with the fluorosurfactant bulk concentration, whereas the fluorocarbon chain is more hydrophobic than and the resulting bilayers have low adhesion energies.
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