Orientation and Order of Aqueous Organic Ions Adsorbed to a Solid Surface

Sukhishvili, Svetlana A.; Granick, Steve

doi:10.1021/jp982565b

Cited by 12 publications

(12 citation statements)

References 45 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…One complication, for the case when the refractive index of the thin layer of adsorbed molecules is different from that of the solvent, is that the E z component of the electric field should be corrected by the ratio of the refractive indices of the solvent and the adsorbed layer. But this correction is minimal, as was shown before for the similar system …”

Section: Methodssupporting

confidence: 62%

See 1 more Smart Citation

How Polyelectrolyte Adsorption Depends on History: A Combined Fourier Transform Infrared Spectroscopy in Attenuated Total Reflection and Surface Forces Study

1999

Self Cite

View full text Add to dashboard Cite

We present a systematic study of how adsorption history affects the thickness, surface forces, and interfacial rheology of a model cationic polymer. The polymer was quaternized poly-4-vinylpyridine, QPVP (weight-average degree of polymerization n w = 325 and 98% quaternized with ethyl bromide). The main comparisons concerned one-step adsorption from solution at a variable salt concentration up to 0.5 M NaCl, versus two-step adsorption (initial adsorption from buffer solution without added salt, then NaCl added later). The aqueous solutions were buffered at pH = 9.2 such that the surfaces (mica in the case of surfaces forces (SFA) experiments, oxidized silicon in the case of in situ infrared (FTIR-ATR) experiments) in each case carried a large negative charge. The SFA and FTIR-ATR experiments gave consistent estimates of the amount of polymer adsorbed, confirming the expectation that adsorption should be driven by electrostatic attraction to the surface of large opposite charge. The adsorbed amount showed little dependence on path, validating the common assumption of equilibration in this respect. However the layer thickness measured by surface forces, the shear nanorheology response at a given surface force, and the dichroism of pendant side groups of the polymer all showed a pronounced dependence on the path to reach the adsorbed state. We interpret the measurements to suggest that two-step adsorption produces an inhomogeneous layer comprised of a dense layer of segments closest to the solid surface and a sparse outer layer. In particular, two-step adsorption produced thicker layers and a greater tendency to decouple shear forces from those that resist compression in the normal direction, thereby lessening the shear forces at a given level of normal force.

show abstract

Section: Methodssupporting

confidence: 62%

“…The influence of a polymer's stereoirregularity precludes quantitative analysis of the dichroism data presented here. The effect is qualitative for a polymer, though for the monomer analogue quantitative interpretation is possible. , …”

Section: Resultsmentioning

confidence: 99%

How Polyelectrolyte Adsorption Depends on History: A Combined Fourier Transform Infrared Spectroscopy in Attenuated Total Reflection and Surface Forces Study

1999

Self Cite

View full text Add to dashboard Cite

show abstract

“…As mentioned in the Experimental Section, to reduce overlap of the infrared spectra of QPVP, PMA, and PSS with those of water itself, we used D 2 O rather than H 2 O as the solvent. Control experiments showed that our results presented below did not depend on the choice of solvent, H 2 O or D 2 O …”

Section: Resultsmentioning

confidence: 64%

“…Control experiments showed that our results presented below did not depend on the choice of solvent, H 2 O or D 2 O. 30 Figure 2 shows the infrared spectra of PMA molecules in aqueous solutions at pH ) 2.0 and 6.0, respectively. Solutions of PMA were exposed to the surface of a Si ATR crystal.…”

Section: Resultsmentioning

confidence: 67%

Local Electrostatics within a Polyelectrolyte Multilayer with Embedded Weak Polyelectrolyte

2002

Self Cite

View full text Add to dashboard Cite

We investigate local electrostatics within a polyelectrolyte multilayer formed from layerby-layer self-assembly of QPVP/PSS (quaternized poly(vinylpyridine)/poly(styrenesulfonate)), through the strategy of embedding, within this multilayer, a weak polyacid, PMA (poly(methacrylic acid)). The methods mainly involved infrared measurements of these multilayer films using FTIR-ATR, Fourier transform infrared spectroscopy in attenuated total reflection, after deposition at several solution concentrations and ionic strength. A key finding is that the ionization of PMA, measured at pH ) 6.0 (near its pK a), executed giant oscillations, between 30% and 80% ionization, each oscillation being in linear proportion to the quantity of strong polyelectrolyte deposited in the outermost layer of the polyelectrolyte multilayer. These oscillations persisted with a decay length (>10 layers) that far exceeded the Debye length of the aqueous solution, suggesting that this long-range electrostatic coupling stemmed from the presence of polyanions and polycations that were fixed in space within the multilayer assembly rather than mobile as supposed in a traditional analysis of screening. In addition, in the process of multilayer formation, the mass adsorbed of the outermost layer was not simply controlled by the excess charge on the preexisting multilayer. Instead, the film became responsive in the sense that its charge adjusted in the direction of maintaining neutrality within the multilayer assembly when additional charges deposited on top. The approach of embedding a weak polyelectrolyte within a multilayer of strong polyelectrolyte may find application in sensor design.

show abstract

“…The intensity of this peak amounted to about 20% of the total intensity of the 1701 cm -1 peak. The curve-fitting procedure was most elaborate in region 3, where apart from a strong carboxylate ion band centered at 1552 cm -1 , there are also low-energy bands associated with the in-plane vibration of the pyridine and pyridinium rings located in the region of 1518−1573 cm -1 . Although the intensity of these peaks amounted to only from 7 to 17% of the intensity of the overlapping band at 1552 cm -1 , it was important to do a careful curve-fitting in order to subtract their intensities from the absorbance of carboxylate groups.…”

Section: Resultsmentioning

confidence: 99%

Ionization and pH Stability of Multilayers Formed by Self-Assembly of Weak Polyelectrolytes

2003

Self Cite

View full text Add to dashboard Cite

The formation of polyelectrolyte multilayers using the layer-by-layer sequential self-assembly of a weak polybase and polyacid onto a surface of Si crystal and their stability under acidic conditions were studied. The system was 12%, 20%, 25%, 37%, 90%, or 98% quaternized poly-4-vinylpyridine (Q12, Q20, Q25, Q37, Q90, or Q98) as polybases (generally abbreviated as QPVP) and poly(methacrylic acid) (PMAA) as a polyacid in buffered D2O. The adsorption and ionization of pyridine rings and carboxylic groups were quantified using Fourier transform infrared spectroscopy in attenuated total reflection mode. At pH ) 5, film growth was primarily controlled by electrostatic interactions. When QPVP was included into the top layer, ionization of carboxylic groups was increased compared to its value in solution. The amount of the induced charge increased linearly with the total charge density of the polybase (calculated as a sum of ethylated pyridinium and protonated pyridinium groups), suggesting the formation of both types of electrostatic pairs (COO --NR + and COO --NH + ). The degree of ionization of both pyridine groups and carboxylic groups within the film responded to the charge of the polymer included in the top layer and oscillated as a function of layer number. The average ionization of the carboxylic groups within the multilayer was suppressed when the multilayer was topped with PMAA, and it was enhanced when the top layer was the polybase. The effect was rather long-ranged and persisted through over three polymer layers with a decay length of about 100 Å. When the pH of the buffer solution was lowered below pH 2, multilayers dissolved due to protonation of carboxylic groups and disruption of polymer/polymer ionic contacts. The multilayer stability under acidic conditions was dependent on the alkylation degree of QPVP. With the exception of the largest alkylation degrees, the stability of the film increased with the alkylation degree of QPVP. The multilayer destruction correlated with the protonation of the small (<5%) residual fraction of carboxylic groups that was included into polymer/polymer ionic pairs and with the number of ionic polymer/polymer contacts per QPVP chain, suggesting that the number of polymer/polymer contacts during self-assembly was a critical parameter in multilayer stability. The results show the effect of the QPVP charge density on the ionization of self-assembled PMAA and on the pH stability of polyelectrolyte multilayers.

show abstract

Orientation and Order of Aqueous Organic Ions Adsorbed to a Solid Surface

Cited by 12 publications

References 45 publications

How Polyelectrolyte Adsorption Depends on History: A Combined Fourier Transform Infrared Spectroscopy in Attenuated Total Reflection and Surface Forces Study

How Polyelectrolyte Adsorption Depends on History: A Combined Fourier Transform Infrared Spectroscopy in Attenuated Total Reflection and Surface Forces Study

Local Electrostatics within a Polyelectrolyte Multilayer with Embedded Weak Polyelectrolyte

Ionization and pH Stability of Multilayers Formed by Self-Assembly of Weak Polyelectrolytes

Contact Info

Product

Resources

About