The Volume Fraction Profile of Terminally Adsorbed Polymers

1991 ◽  
Vol 248 ◽  
Author(s):  
R. J. Composto ◽  
T. Mansfield ◽  
G. Beaucage ◽  
R. S. Stein ◽  
D. R. Iyengar ◽  
...  
Keyword(s):  
Concentration Profile ◽  
Volume Fraction ◽  
Neutron Reflectivity ◽  
Similar Molecular Weight ◽  
Parabolic Profile ◽  
Grafting Density ◽  
Tethered Chains ◽  
Adsorbed Polymers ◽  
Unperturbed Dimension ◽  
Poor Solvent

AbstractWe have used neutron reflectivity to measure the concentration profile of carboxylic acid-terminated polystyrene at the liquid/solid interface. Two isotopic systems were studied: (1) deuterated polystyrene (DPS) in cyclohexane and (2) polystyrene (PS) in deuterated cyclohexane. Although measured at 24°C (a poor solvent condition), the high grafting density of PS tethered chains causes the chains to weakly stretch to 3-5 times its unperturbed dimension. Although of similar molecular weight, the height of the DPS layer is about 50% higher than that of the PS. In both systems, the volume fraction of polymer near the wall is ∼ 0.60. For the DPS system, reflectivity profiles can be simulated using a parabolic profile with a depletion layer at the silicon-liquid interface. However, in the PS system, no depletion is observed. Here, the shape. of the PS concentration profile is parabolic with a rounded tail.

Chemical grafting of silane end-functionalized polymer on silicon surfaces

1993 ◽  
Vol 304 ◽  
Author(s):  
A Karim ◽  
S. K. Satija ◽  
W. Orts ◽  
J. F. Ankner ◽  
C. F. Majkrzak ◽  
...  
Keyword(s):  
Concentration Profile ◽  
Polymer Concentration ◽  
Silicon Surfaces ◽  
Low Molecular Weight ◽  
Neutron Reflectivity ◽  
Exponential Behavior ◽  
Kinetics Of Adsorption ◽  
Chemical Grafting ◽  
Kinetics Of ◽  
Poor Solvent

AbstractX-ray and neutron reflectivity was used to determine the kinetics of adsorption and characterize the concentration profile of a low molecular weight trichlorosilane endfunctionalized polystyrene adsorbed onto polished silicon wafers. Higher adsorbed amounts were obtained from a cyclohexane solution of the polymer rather than toluene, with kinetics that followed a stretched exponential behavior. For moderately high grafting densities the polymer concentration profile in deuterated toluene (a good solvent) was best modelled using a small tailed parabola. In deuterated cyclohexane (a poor solvent) the brush profile steepened but was substantially smoother than a step, while in D20 (a non-solvent) it became step-like.

scholarly journals Influence of the Architecture of Soft Polymer-Functionalized Polymer Nanoparticles on Their Dynamics in Suspension

Polymers ◽  
2020 ◽  
Vol 12 (8) ◽  
pp. 1844
Author(s):  
Young-Gon Kim ◽  
Waraporn Wichaita ◽  
Héloïse Thérien-Aubin
Keyword(s):  
Correlation Time ◽  
Nmr Relaxation ◽  
Thick Layer ◽  
Polymer Chains ◽  
The Core ◽  
Grafting Density ◽  
Tethered Polymer Chains ◽  
Close Proximity ◽  
Soft Polymer ◽  
Tethered Chains

The behavior of nanogels in suspension can be dramatically affected by the grafting of a canopy of end-tethered polymer chains. The architecture of the interfacial layer, defined by the grafting density and length of the polymer chains, is a crucial parameter in defining the conformation and influencing the dynamics of the grafted chains. However, the influence of this architecture when the core substrate is itself soft and mobile is complex; the dynamics of the core influences the dynamics of the tethered chains, and, conversely, the dynamics of the tethered chains can influence the dynamics of the core. Here, poly(styrene) (PS) particles were functionalized with poly(methyl acrylate) (PMA) chains and swollen in a common solvent. NMR relaxation reveals that the confinement influences the mobility of the grafted chain more prominently for densely grafted short chains. The correlation time associated with the relaxation of the PMA increased by more than 20% when the grafting density increased for short chains, but for less than 10% for long chains. This phenomenon is likely due to the steric hindrance created by the close proximity to the rigid core and of the neighboring chains. More interestingly, a thick layer of a densely grafted PMA canopy efficiently increases the local mobility of the PS cores, with a reduction of the correlation time of more than 30%. These results suggest an interplay between the dynamics of the core and the dynamics of the canopy.

Neutron reflectivity of end grafted polymers in poor solvent: Kinetic effects

1996 ◽  
Vol 221 (1-4) ◽  
pp. 337-341 ◽  
Author(s):  
D. Perahia ◽  
D.G. Wiesler ◽  
S.K. Satija ◽  
L.J. Fetters ◽  
S.K. Sinha ◽  
...  
Keyword(s):  
Neutron Reflectivity ◽  
Grafted Polymers ◽  
Kinetic Effects ◽  
Poor Solvent

Surface Enrichment and Evaporation in a Polymer Mixture of Long and Short Chains

1989 ◽  
Vol 166 ◽  
Author(s):  
Russell J. Composto ◽  
Richard S. Stein ◽  
Gian P. Felcher ◽  
Abdelkader Mansour ◽  
Alamgir Karim
Keyword(s):  
Molecular Weight ◽  
Film Thickness ◽  
Concentration Profile ◽  
Scattering Length ◽  
Weight Fraction ◽  
Polymer Mixture ◽  
Light Chains ◽  
Neutron Reflectivity ◽  
Surface Enrichment ◽  
Polymer Interface

ABSTRACTNeutron reflectivity has been used to determine the concentration profile at the vacuum-polymer interface for a two polymer blend. To quantify surface enrichment and evaporation due to differences in chain length, we have measured the reflectivity of a mixture of short deuterated and long protonated polystyrene chains (DPS & PS), with a weight fraction of 0.5. When a mixture of DPS and PS chains of molecular weight 720 and 910k respectively were annealed, a small but measurable increase in asymptotic reflectivity occured, coupled with a decrease of film thickness and scattering length density. This is indicative of surface enrichment and evaporation of the light chains (DPS). Ellipsometry studies confirmed that the short chains evaporated and its rate was established as a function of the temperature. Upon increasing the DPS molecular weight to 9600, the enrichment becomes considerably greater whilst the evaporation becomes negligible.

Asphaltene Aggregation Kinetics in Crude Oil Using Confocal Microscopy

2001 ◽  
Vol 7 (S2) ◽  
pp. 542-543
Author(s):  
Robert J. Johnston ◽  
Thomas G. Mason
Keyword(s):  
Crude Oil ◽  
Laser Scanning ◽  
Volume Fraction ◽  
Laser Scanning Microscopy ◽  
Confocal Laser ◽  
Heavy Crude Oil ◽  
Aggregation Kinetics ◽  
Heavy Crude ◽  
Poor Solvent ◽  
Microscope Stage

Confocal laser scanning microscopy (CLSM) has been used to study asphaltene aggregation kinetics by employing the microscope's automated acquisition to generate time-lapsed projection maps of aggregating asphaltenes in the autofluorescent matrix of crude oil. Heavy crude oils contain asphaltene particles resulting in the production of optically observable micron-sized asphaltene aggregates. These aggregates form as a result of attractive interactions induced by mixing the heavy crude oil with a poor solvent. This technique has been employed to determine the volume fraction of aggregated asphaltenes, ϕagg, and the time evolution of this phenomenon. The measurements cover a range of various concentrations of asphaltene volume fractions of the heavy asphaltenic oil, ϕm, from ϕm =0.001 to ϕm =0.4.At each ϕm,after the mixtures have been made, approximately 20 μl of the crude oil is placed in a 20 μm deep flat-well quartz cell and immediately placed on a microscope stage.

scholarly journals AIE phenomena of a cyanostilbene derivative as a probe of molecular assembly processes

2017 ◽  
Vol 196 ◽  
pp. 231-243 ◽  
Author(s):  
Fuyuki Ito ◽  
Jun-ichi Fujimori ◽  
Narumi Oka ◽  
Michel Sliwa ◽  
Cyril Ruckebusch ◽  
...  
Keyword(s):  
Fluorescence Spectra ◽  
Volume Fraction ◽  
Binary Solution ◽  
Molecular Assembly ◽  
Multivariate Curve Resolution ◽  
Crystal Formation ◽  
Curve Resolution ◽  
Solvent Water ◽  
The Poor ◽  
Poor Solvent

The initial processes of the crystallization of a solute molecule, 1-cyano-trans-1,2-bis-(4′-methylbiphenyl)-ethylene (CN-MBE) in binary solution (water and acetone), were investigated by means of fluorescence spectroscopy as well as scanning electron microscopy (SEM). With an increase in the volume fraction (Vw) of the poor solvent (water) in the solution, a drastic change in the fluorescence spectra and intensity of CN-MBE was observed. This change was attributed to aggregation induced emission (AIE). By analyzing the evolution of AIE by multivariate curve resolution-alternating least squares (MCR-ALS), it was revealed that four main species appeared in the solution depending on the Vw values. On the basis of molecular exciton theory, we assigned these four emissive states to the monomer, H-dimer, J-dimer, and H-aggregates. Interestingly, the J-dimer state was observed only in a Vw range of 40% to 50%, just before the formation of the aggregate. This result suggests that the J-dimer plays an important role as the precursor for larger aggregates leading to crystal formation. By integrating the present results with previous work on the crystallization of CN-MBA through solvent evaporation, we discussed the dynamics of the crystallization from the viewpoint of the sequence of molecular species appearing in the aggregation in solution.

Multi-Block Copolymers in Selective Solvent: A Brownian Dynamics Simulation

2004 ◽  
Vol 856 ◽  
Author(s):  
Yongsheng Liu ◽  
Huifen Nie ◽  
Rama Bansil ◽  
Zhenli Zhang ◽  
Sharon Glotzer
Keyword(s):  
Brownian Dynamics ◽  
Volume Fraction ◽  
Dynamics Simulation ◽  
Multiblock Copolymers ◽  
Brownian Dynamics Simulation ◽  
Selective Solvent ◽  
Bcc Lattice ◽  
Dynamics Simulations ◽  
Brownian Dynamics Simulations ◽  
Poor Solvent

ABSTRACTWe performed Brownian Dynamics simulations of multiblock copolymers of A and B polymers in a solvent selective for the A block at a volume fraction of 20%. Tri-, penta- and heptabocks were simulated. Fourier transformation reveals micellar clusters arranged in a BCC lattice, in agreement with scattering experiments. The clusters were analyzed using a percolation approach and we observed larger clusters when the outermost block was in the poor solvent condition. The ratio of number of loops to bridges decreases as the number of blocks in the copolymer increases, as does the polydispersity. Increased penalty of looping as the number of blocks increases leads to a larger number of smaller clusters with more bridges.

scholarly journals Reflectivity Studies on Adsorbed Block Copolymers Under Shear

1994 ◽  
Vol 376 ◽  
Author(s):  
Gregory S. Smith ◽  
Stephen Wages ◽  
Shenda M. Baker ◽  
Chris Toprakcioglu ◽  
George Hadziioannou
Keyword(s):  
Diblock Copolymers ◽  
Quartz Substrate ◽  
Neutron Reflectivity ◽  
Shear Rates ◽  
Poly Ethylene Oxide ◽  
Poly Ethylene ◽  
Reflectivity Data ◽  
Static Conditions ◽  
Anchor Block ◽  
Poor Solvent

ABSTRACTWe report neutron reflectivity data on (poly)styrene-(poly)ethylene oxide (PS-PEO) diblock copolymers adsorbed onto quartz from the selective solvent deuterated cyclohexane (a non-solvent for PEO and a poor solvent for PS). The PEO "anchor block" adsorbs strongly to form a thin layer on the quartz substrate, while the PS chains dangle into the solvent. We find that under static conditions the density profile of the PS block in a poor solvent can be well described by a Schultz function which is indicative of a polymer "mushroom." Furthermore, we have studied the same system under shear at shear rates from 0-400s-l. We find that there is a dramatic increase in the thickness of the PS layer under shear in cyclohexane and that the relaxation time from the shear-on profile back to the static profile is on the order of several days.

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