Search

原发性心脏淋巴瘤（PCL）极为罕见，仅占心脏肿瘤的1%~2%，最常见的病理类型为弥漫大B细胞淋巴瘤（DLBCL）。DLBCL多发于右心房，其次为右心室。临床表现包括心力衰竭、心包积液、上腔静脉压迫综合征、心律失常，可出现发热等全身症状。该文报道1例经静脉右心房肿瘤活检确诊原发性心脏DLBCL患者，根据病理分型，指导靶向化疗后病情完全缓解，预后良好。.

To explore the role of HOTAIR in the pathogenesis of adrenocortical carcinoma (ACC) and its underlying mechanism.Differentially expressed lncRNA (HOTAIR) in ACC was screened out from the GEO database. The survival analysis and ROC curve were performed according to HOTAIR expressions in ACC patients. The correlation between HOTAIR expression and clinical information of ACC patients was analyzed by chi-square test. The univariate and multivariate COX regression analysis was carried out to analyze the relationship between HOTAIR expression, disease-free survival (DFS) and overall survival (OS) of ACC patients. We then detected HOTAIR expression in 77 ACC tissues and 30 normal tissues by qRT-PCR (quantitative Real-time polymerase chain reaction). ACC cell lines were further screened out for the following in vitro experiments. After altering HOTAIR expression in ACC cells by plasmid transfection, proliferation and cell cycle were detected by Cell Counting Kit-8 (CCK-8) and colony formation assay, respectively. Finally, Western blot was utilized to detect expressions of cell cycle-related genes in ACC cells.HOTAIR was overexpressed in ACC tissues than that of normal tissues. HOTAIR expression was remarkably increased in ACC with T3 and T4 stage than that of T1 and T2 stage. Moreover, HOTAIR expression was remarkably increased in ACC with stage III and IV than that of stage I and II. HOTAIR was an independent prognostic factor for DFS and OS of ACC patients. For in vitro experiments, inhibited proliferation and arrested cell cycle were observed in H295R cells transfected with si-HOTAIR. Opposite results were obtained after SW-13 cells were transfected with HOTAIR overexpression plasmid. Furthermore, expressions of cell cycle-related genes, including Cyclin D1, p-Rb and p-GSK3β were remarkably decreased after HOTAIR knockdown.We demonstrated for the first time that HOTAIR is overexpressed in ACC and is a prognostic risk factor in ACC patients. HOTAIR participates in the development and progression of ACC via shortening cell cycle and promoting proliferation of ACC cells.

Wetting behaviour of a Cu/Ti3SiC2 system was investigated by the sessile drop technique under a vacuum atmosphere. Contact angles between Cu and Ti3SiC2 changed from 95 to 15° as temperatures increased from 1089 to 1270°C. Two distinct reaction layers consisting of different contents of Cu, TiCx, Ti3SiC2 and CuxSiy intermetallics were formed at the interface of Cu and Ti3SiC2. The formation of the interface layers contributes to the improvement of the wettability of the system. The dissolution of Si from theTi3SiC2 into the molten Cu at high temperature plays a dominant role in the wetting behaviour of Cu/Ti3SiC2 systems.

Neutron reflection and surface tension have been used to study the adsorption of the nonionic surfactant monododecyl hexaethylene glycol (C 12 E 6 ) and the mixed nonionic–anionic surfactants n -dodecyl triethylene glycol (C 12 E 3 ) and Sodium dodecyl sulfate (SDS) at the air–liquid interface. Water and a sorbitol ( d -glucitol, CH 2 OH(HCOH) 4 CH 2 OH)/water mixture were selected as the solvents. The addition of 300 g/liter of sorbitol to an aqueous solution of C 12 E 6 reduces the critical micellar concentration, cmc, from ∼7 × 10 −5 to ∼3 × 10 −5 M, and increases the surface pressure at the cmc; the effect on the C 12 E 3 /SDS mixture is less. Despite these changes, the pattern of adsorption at the air–liquid interface is essentially unaltered by the addition of sorbitol, and the surface tension and neutron reflectivity data are in good agreement. The consequences of the sorbitol addition are however seen directly in the structure of the C 12 E 6 monolayer. The ethylene oxide (EO) chain is more extended than in water, and more displaced from the solvent, consistent with dehydration of the ethylene oxide group.

The structure of mixed monolayers of the zwitterionic phospholipid dipalmitoylglycerophosphocholine (DPPC) containing nonionic surfactants of the polyethylene glycol monododecyl ether variety (C12En with n = 2, 4, 6, 8) is studied at the air/water interface using a combination of neutron reflectivity with film balance techniques. The two methods applied simultaneously gave good agreement of the molecular area data using the most simple single-layer model for fitting the reflectivity curves. Isotopic substitution of both lipids and surfactants has been employed in order to determine structural parameters of both components separately. All measurements were done at lipid to surfactant molar ratios rL/S > 2 and at surfactant concentrations well below their critical micelle concentration. Measurements were performed in the liquid-condensed (LC) and in the liquid-expanded (LE) phase states of the monolayer. The results show that all surfactants studied readily associate with the DPPC in the LE phase to a mixed monolayer but get completely transferred from the monolayer into the subphase at the transition to the LC phase. A determination of the surfactant partition between the mixed monolayer and subphase at the LE phase state provides evidence that virtually all surfactant is associated with the monolayer. The area per surfactant molecule in the mixed monolayer is found to increase rather linearly from 45 ± 5 Å2 (n = 2) to 165 ± 5 Å2 (n = 8) by an increment of 22 ± 2.5 Å2 per ethylene glycol group (film pressure 5 mN/m). The thickness of the surfactant alkyl chain was found to be 14 ± 2 Å for C12E2 and 8 ± 2 Å for C12E4 which indicates a very high degree of chain disorder. The thickness of the fatty acyl region of the DPPC is not affected by the surfactant for n = 2 and 4. The headgroup region thickness of the mixed monolayer is 14 ± 2 Å for C12E2 and 11 ± 2 Å for C12E4. While the diethylene glycol group exhibits a rather extended conformation, longer surfactant headgroups are prone to a significant incidence of gauche conformations. Moreover, the data indicate that the interaction of C12En with the monolayer is markedly different for n = 2 compared to all other ethylene glycol groups (n = 4, 6, 8) studied. © 1994 American Chemical Society.

`Imaka is a ground layer adaptive optics (GLAO) demonstrator on the University of Hawaii 2.2m telescope with a 24'x18' field-of-view, nearly an order of magnitude larger than previous AO instruments. In 15 nights of observing with natural guide star asterisms ~16' in diameter, we measure median AO-off and AO-on empirical full-widths at half-maximum (FWHM) of 0''95 and 0''64 in R-band, 0''81 and 0''48 in I-band, and 0''76 and 0''44 at 1 micron. This factor of 1.5-1.7 reduction in the size of the point spread function (PSF) results from correcting both the atmosphere and telescope tracking errors. The AO-on PSF is uniform out to field positions ~5' off-axis, with a typical standard deviation in the FWHM of 0''018. Images exhibit variation in FWMM by 4.5% across the field, which has been applied as a correction to the aforementioned quantities. The AO-on PSF is also 10x more stable in time compared to the AO-off PSF. In comparing the delivered image quality to proxy measurements, we find that in both AO-off and AO-on data, delivered image quality is correlated with `imaka's telemetry, with R-band correlation coefficients of 0.68 and 0.70, respectively. At the same wavelength, the data are correlated to DIMM and MASS seeing with coefficients of 0.45 and 0.55. Our results are an essential first step to implementing facility-class, wide-field GLAO on Maunakea telescopes, enabling new opportunities to study extended astronomical sources, such as deep galaxy fields, nearby galaxies or star clusters, at high angular resolution., Comment: 19 pages, 16 figures

Small-angle neutron scattering has been used to study the structure and composition of mixed ionic-nonionic surfactant micelles. A comparison between two different mixed surfactant systems, sodium dodecyl sulfate (SDS) and hexaethylene glycol monododecyl ether (C12EO6) and hexadecyltrimethylammonium bromide (C16TAB) and C12EO6, both in 0.1 M NaCl, has been made. In the latter system, ideal mixing is observed, and in the former, departure from ideality, broadly consistent with regular solution theory, RST, is observed. The deviations from the predictions of RST are attributed to subtle changes in the packing of the two surfactants in the mixed micelles. For the SDS/C12EO6 mixture, the micellar aggregation number is essentially constant with composition and concentration, whereas for the C16TAB/C12EO6 mixture there is a marked micellar growth with increasing concentration and mole fraction of C12EO6 in solution. The SANS results on structure and composition are compared with the results reported for other mixed surfactant systems and are discussed in the context of recent theoretical developments. © 1999 American Chemical Society.

The interactions between poly(ethylene oxide) (PEO) and dodecyl sulfate with different monovalent metal cations (MDS, M = Li+, Na+, Cs+) and dodecyltrimethylammonium bromide (C12TAB) have been stud...

The compositions of the air/solution interface of aqueous mixtures of lithium dodecyl sulfate (LiDS) and cesium dodecyl sulfate (CsDS) with poly(ethylene oxide) (PEO) have been studied as a function of surfactant concentration using neutron specular reflection. Comparison of the results with those for NaDS shows that for all three ionic species the polymer is progressively displaced from the surface on the addition of surfactant until it can no longer be directly detected at the critical aggregation concentration (area per segment > 80 Å2). Comparison of the behavior of the three surfactants with each other and with measurements on the noninteracting combination dodecyltrimethylammonium bromide (C12TAB)/PEO shows that the anionic surfactants interact favorably with PEO at the surface. The additional free energies of binding of surfactant to the surface in the presence of PEO exactly parallel the polymer/micelle binding free energies. Of the three anionics LiDS interacts most strongly, and this is also manifested in adsorption of the PEO at concentrations above the critical micelle concentration of LiDS.

Neutron reflection and surface tension measurements have been used to show that the surface properties of sodium bis(2-ethylhexyl)sulfosuccinate (Aerosol-OT or AOT) at concentrations below the critical micelle concentration (cmc) are dominated by divalent ion impurities. Previous determinations of the area per molecule at the cmc using surface tension measurements and the Gibbs equation have given values of about 100 A2 or higher. Neutron reflection gives a lower value of 78 ± 3 A2. A similar value can be obtained from surface tension measurements only in the presence of species which remove divalent ions from the solution. This suggests that the lower value is much closer to the correct value and that surface tension measurements on AOT will usually give misleading values of the coverage.

Neutron reflection has been used to study the composition of layers of sodium dodecyl sulfate (SDS) and dodecanol mixtures adsorbed at the air/water interface. Saturation of the surface by dodecanol at a 6.7 mM SDS concentration occurs when the bulk dodecanol concentration is about four times the solubility of dodecanol in pure water, indicating that even below the cmc dodecanol is solubilized by SDS. At a fixed dodecanol/SDS ratio the adsorption of dodecanol passes through a maximum at about half the cmc as the SDS concentration is changed, dropping sharply, although not to zero, at the cmc. Above the cmc it is estimated that an average of about two dodecanol molecules are incorporated into a single micelle. The adsorption of SDS is affected by the presence of dodecanol. At low SDS concentrations (

Samples of culture freshwater milkfish (Chanos chanos) from five ponds surrounding open-air waste incineration sites and from five markets in southern Taiwan were analyzed for PCDDs, PCDFs and coplanar PCBs (Co-PCBs). The total TEQ concentration of three chemicals in fish meat was in a wide range of 0.195 to 153 pg/g wet weight. In addition, the bioconcentration factors from sediment to fish meat and crab hepatopancreas biota were arranged in order of Co-PCBs ⪢ PCDFs > PCDDs and Co-PCBs > PCDFs ⪢ PCDDs, respectively.

High resolution inelastic neutron scattering spectra of CH4, CH4/CD4 mixtures, and CH3D adsorbed on exfoliated graphite at 4.5 K have been obtained. The resolution used was approximately five times higher than previously used and has revealed extra detail in the spectra. For CH4 it is shown that the parameter, H, related to rotation about the twofold axes is not exactly zero. It has an unexpected small positive value. For a 1:2 CH4/CD4 mixture the tunneling spectra of the CH4 show that the mixture must be ordered at 4.5 K and that the barriers to rotation of the CH4 are increased slightly when the surrounding CH4 molecules are replaced by the heavier CD4. For CH3D the higher resolution spectra make it possible to make an unambiguous assignment of the tunneling spectra, which is different from that previously proposed. The assignment indicates that there are terms in the orientational potential higher than the threefold Fourier components previously assumed, but that these probably do not affect the derive...

Sediment samples from nine culture ponds for freshwater fish at and near waste incineration sites for metal reclamation in Wan-Li, southern Taiwan, Republic of China were analyzed for PCDDs and PCDFs by HRGC-HRMS. Four of nine samples were heavily polluted by PCDDs and PCDFs, indicating the latter to be dominant. The total TEQ concentrations of PCDDs and PCDFs in the four samples were in the range of 257 to 12200 pg/g dry weight. In addition, the levels corresponded to those of surface soil samples from the same waste combustion areas.

We present a new geometric distortion model for the narrow-field mode of the near-infrared camera (NIRC2) fed by the adaptive optics system on the W. M. Keck II telescope. The adaptive optics system and NIRC2 camera were realigned on 2015 April 13. Observations of the crowded globular cluster, M53, were obtained before and after the realignment to characterize the geometric field distortion. The distorted NIRC2 positions of M53 stars were compared with precise astrometry of this cluster from Hubble Space Telescope observations. The resulting distortion map constructed just before the realignment is consistent with the previous solution derived using data from 2007 to 2009, indicating that the distortion has been stable to ~0.5 mas. The distortion map changed significantly after a realignment of 4.5 mas (75%) rms, and the new distortion model for post-realignment observations have a total accuracy of ~1.1 mas.

We have determined the structure of a monolayer of dodecyltrimethylammonium bromide (C12TAB) adsorbed at the air/water interface at three surface concentrations corresponding to areas per molecule of 44,48, and 60 A 2 , using neutron reflection. We have used isotopic labeling to distinguish the hydrocarbon chain, head group, and solvent distributions. We have also labeled the two halves of the hydrocarbon chain to obtain information about the mean conformation of the chain. At the highest surface concentration we find that the inner half of the chain (next to the head group) is oriented closer to the surface normal than the outer half of the chain indicating that chain defects contribute to the chain structure. We also find that the surfactant layer is substantially rougher than that predicted from the simple capillary wave model of pure liquid. We have compared the structure of the different C n TABs with chain lengths varying from C 12 to C 18 at an area per molecule of about 44 A 2 and from C 10 to C 16 at an area per molecule close to 60 A 2 . The most remarkable observation about the lower area measurements is that the thickness of the layer is the same for the four chain lengths even though the extended length of the chain increases by 50%. When account is taken of surface roughness, the intrinsic thickness of the chain region of the monolayer is also constant and for C 18 is less than half the extended length. Comparison of the thickness of the layer and the separation of the chain and head distributions indicates that the mean orientation of the outer half of the chain is further from the surface normal than is the inner half of the chain, and this difference increases with chain length. At the higher area per molecule the C 10 TAB forms the thickest layer and this is associated with the chains being closer to the surface normal than for the other C n TABs.

The structure of layers of triethylene glycol monododecyl ether (C12E3) adsorbed at the air/water interface at four concentrations from the critical micelle concentration (cmc = 5.5 × 10-5 M) down to 1 × 10-6 M have been determined using neutron specular reflection together with isotopic substitution. The distribution of any part of the layer is described in terms of the full width of the distribution at half height, σ; i.e., σ is a measure of the thickness of that part of the layer. The width, σ, of the alkyl chain part of the layer varied from 14 ± 1 A at an area per molecule (A) of 36 A2 down to 10 ± 1.5 A at an A of 89 A2. The corresponding widths of the ethylene glycol region varied from 13 ± 1 to 5 ± 2 A, and the separation of the two chain regions changed from 8 ± 0.5 to 4.5 ± 1 A. The separation of the alkyl chains from the midpoint of the water distribution was found to be 2 A greater than from the ethylene glycol chains at the cmc but exactly the same at 1 × 10-6 M. Isotopic labeling of the two halves of the alkyl chain was used to establish that the alkyl chain is substantially tilted away from the surface normal at all concentrations and that at least one gauche conformation occurs on average in the alkyl chain at the highest surface concentration. The shape of the overall chain distribution is better described by a Gaussian distribution than by a uniform layer. The static displacement of the surfactant molecules in the direction normal to the surface is shown to be strongly disordered at the cmc, the mean displacement being about 9 A, which is of the order of half the projected length of the molecule in the vertical direction. The ethylene glycol chain is oriented close to the normal direction when A = 36 A2 but seems to lie nearly flat in the surface plane when A = 89 A2.

Surface soil samples from six sites at which waste electric wires and/or magnetic cards are incinerated for metal reclamation in Taiwan, Republic of China, were analyzed for polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). All samples analyzed were contaminated with PCBs at a level of 0.45 to 77 ug/g dry weight, PCDDs at n.d. to 540 ng/g and PCDFs at 1.8 to 310 ng/g. The samples from the incineration sites only with waste electric wire were heavily polluted by these chlorinated chemicals.

The composition and structure of soluble monolayers of cationic surfactants of alkyltrimethyl ammonium bromide adsorbed at the air-water interface have been studied by the neutron reflection technique. — At the critical micelle concentration (CMC) the area per surfactant molecule was found to be 55 ± 3 A2 for decyl trimethyl ammonium bromide (C10TAB), 48 ± 3 A2 for tetradecyl trimethyl ammonium bromide (C14TAB), and 43 ± 3 A2 for octadecyl trimethyl ammonium bromide (C18TAB). — The determination of the structure of the surfactant layers at their corresponding CMC was based on three differnt isotopic combinations of water and surfactant. The results were analysed using both optical matrix method and the kinematic approach. The thickness of the whole surfactant monolayer was found to be 19 ± 2 A for C10TAB, 22 ± 2 A for C14TAB and C18TAB. The thickness of alkyl chain layer out of water was found to be 11 ± 1 A for C10TAB and 12.5 ± 1 A for the two other surfactants. The amount of alkyl chain immersed in water was found to be 30 – 40%, with shorter chain surfactants being more immersed.

A three-dimensional space-time model has been established for pressurized water reactor rod ejection analyses. Core neutronics is modeled with the two-group neutron diffusion equation and formulated in a coarse-mesh finite difference form. The time-dependent solution is obtained using a two-step alternating direction semi-implicit method. Nuclear data are processed from the CASMO cross-section library. Fuel temperature is calculated using finite differenced radial heat conduction equations. Core thermal hydraulics is described using the COBRA code

When rabbits acutely exposed to hypobaric hypoxia (at imitative altitude 5,000 m, PaO2 = 6.7 kPa), the percentage of the activity of superoxide dismutase (SOD in erythrocyte; EC 1.15.1.1) decreased respectively to 86%, 76%, 81%, 84%, 55%, 81%, 84% and 95% for a period of 0.25, 0.5, 1, 2, 3, 4, 5 and 24 h hypoxia while MDA (malondialdehyde) in erythrocyte and plasma increased significantly during hypoxia periods of 1, 2, 3, 5 and 24 h (n = 5, P0.05, P0.01 vs. normoxia group). The increase of MDA in plasma could be prevented by vitamin E (V. E, i.p, 1 mg daily for 3 consecative days before hypoxia), but that in erythrocyte did not show significant change probably because the injected V.E. without vehicle cannot penetrate through the erythrocyte membrane effectively. The echinocytes from erythrocytes increased significantly after hypoxia for 24 h (n = 5, P0.05 vs. normoxia group). However, by injecting MPEG-SOD (monomethoxypolythlene glycol-SOD) intravenously 30 min before hypoxia, the increase of MDA (both of erythrocyte and plasma) and echinocytes (from erythrocytes) were both inhibited obviously during hypoxia for 24 h (n = 5, P0.05, P0.01 vs. hypoxia group). It is inferred that the increase of MDA and echinocytes from erythrocytes may be due to lipid peroxidation by superoxide free radicals (O2-.) generated in erythrocytes through Fenton pattern Haber-Weiss reaction during hypobaric hypoxia.

Neutron reflectometry has developed into a powerful method for studying the structure of a wide variety of interfaces involving solids, liquids, and polymers. The basis of the method is described in terms of the kinematic approximation, which allows a direct connection to be made between neutron reflectivity and the structure factor across the interface. The use of isotopic substitution to break down the structure factors into partial structure factors is then described. As an experimental example, the interface between a surfactant solution and air is analysed in detail to show how an analysis in terms of partial structure factors may be used to derive information directly about interfacial structure with minimal reliance on model fitting. A further example of the determination of structure of an adsorbed layer at the solid/liquid is then considered.

Spectra neutron reflection has been used to determine the adsorption of sodium dodecyl sulfate (SDS) and n-dodecyl triethylene glycol (C12E3) at the air-solution interface at a fixed bulk composition ratio (65 mol % C12E3) over a wide range of concentrations in excess of the critical micelle concentration. The results are compared with those obtained from the application of regular solution theory to surface tension data for the same system. The proportion of SDS in the absorbed layer is in good agreement with the theoretical predictions.

Neutron reflectivity with isotopic substitution has been used to determine directly the mean separation between the center of the distribution of a hydrophobic chain of a surfactant adsorbed at the air/water interface and the mean position of the aqueous surface. The method is described and applied to the study of three surfactant layers, sodium dodecyl sulfate, tetradecyltrimethylammonium bromide, and triethylene glycol monododecyl ether, all adsorbed from solution at concentrations close to their critical micelle concentrations. The separations are found to be, respectively, 7.5,8.0, and 10.5 ± 1 angstrom. This result is shown to be independent of detailed assumptions about the structure of the layer. Comparison of these values with the width of the chain and solvent distributions shows that the hydrocarbon chain is significantly immersed (30%) in the water.

The purposes of this study were to give the characteristics of viridans streptococci isolated from dental plaque, and the relationships with dental caries. We stained 69 patients' teeth on supragingival plaques (Plaque Index = 1) with the Pfiffer's reagent or FDC RED#28 dye, then isolated 80 strains of oral streptococci from 69 patients. Cultures were grown in TSB, MS, and MSB media. A total of 80 fresh-isolated plaque streptococci, including strains of S. salivarius, S. sanguis, S. mitis, and S. mutans were identified on the basis of morphologic, dark field, SEM, and biochemical characteristics. All of the oral plaque streptococci were to be found in significant percentages in dental plaque. Patients who had caries harboured S. mutans more often (37/40) than patients without caries (7/29). S. mutans comprised the greatest percentage (37/69) of microorganisms encountered in caries' plaque, and there was an association between high counts of S. mutans and the presence of dental caries. Cultural and biochemical methods were used for the isolation and identification of the different species of S. mutans. The result indicated that biotype I were the most predominant species (50%) in dental plaque. Thus, it is possible to isolate, screen and identify unknown strains through the morphologic, darkfield, SEM, and biochemical characteristics of viridans streptococci isolated from human dental plaque. By means of the present methods for identification, we hold considerable promises for contributing to the prevention and diagnosis of dental diseases.

The types of 59 isolates of adenovirus (Adv) which were isolated between winter, 1984 and spring, 1986 were identified by type-specific monoclonal antibodies (McAb) against Adv types 3 and 7. The results showed that the method could not only identify the types of Adv, but also discover the changes of their subtypes with time. The tedious neutralization test can be replaced by this simple method.

Two new C21 steroidal constituents, named otophylloside A(IV) and otophylloside B(V), have been isolated from the roots of Cynanchum otophyllum Schneid, whose structures have been analysed in this paper by using X-ray crystallography and spectrometric data (UV, IR, 1H- and 13C-NMR, MS) and chemical reaction. They were found to be active against epilepsy, IV and V can protect rats from audiogenic seizures (AS) and its ED50 = 10.20 mg/kg.

Neutron reflectivity with isotopic substitution has been used to determine directly the structure of triethylene glycol monododecyl ether adsorbed at the air-water interface. The surface excess has been measured from concentrations ranging from twice the critical micelle concentration (cmc) (=5.5 × 10-5 M) to one fiftieth the cmc. The results are in good agreement with those from surface tension measurements and show that the area per molecule tends to a limiting value of 36 Å2. The structure of the adsorbed layer has been determined at four concentrations: cmc, 0.2 cmc, 0.0545 cmc, and 0.0182 cmc. Two different methods of analysis of the data have been employed. One is the optical matrix method which fits a single structural model to the reflectivity profiles from a set of isotopic species at a given concentration and the other is a more direct approach based on the kinematic theory. The two methods give structures identical within experimental error. The variation of the thicknesses of the hydrocarbon chain region of the adsorbed layer and the region where solvent has a density less than its bulk value (approximately described as the head group region) and the relative locations of chain and water distributions across the surface with bulk concentration have been determined. For the saturated monolayer at the cmc the thickness of the chain region is found to be 20 ± 1 Å, that of the head group region to be 11 ± 1 Å, and that of the mean center to center distribution of chains and water to be 10 ± 1 Å. The number of water molecules associated with each surfactant molecule is 6. At the lowest concentration (0.0182 cmc) where the monolayer is at its most dilute, it is found that the thickness of the whole layer is 15 ± 1 Å, that of the head regions is 7 ± 1 Å, and the separation of the two distributions is 5 ± 1 Å, with the number of water molecules per surfactant now about 10. Comparison of these values with the width of the chain and solvent distributions shows that the immersion of the hydrocarbon chains in the water varies from about 25% at the cmc to 40% at 0.0182 cmc. © 1993 American Chemical Society.

The surface excess of sodium dodecyl sulfate (SDS) in aqueous solutions of SDS and the polymer poly-(vinylpyrrolidone) (PVP) has been measured as a function of SDS and PVP concentrations using neutron reflection. Below the critical aggregation concentration (CAC) the adsorption of SDS is increased by the presence of PVP, indicating that the two components interact cooperatively at the surface. Between the CAC and the critical micelle concentration (CMC) of the surfactant there is a slight depletion of SDS from the surface. Comparison of coverages determined by neutron reflection with those from earlier radiotracer work indicates that, in the higher concentration range, PVP is bound to the surfactant layer, creating a region from which surfactant is depleted, which is further evidence for a strong polymer/surfactant interaction at the surface. Comparison of the effect of added PVP on the surface tension with the neutron reflection measurements indicates that, even below the CAC, the surfactant complexes to the polymer to some extent in the bulk solution. There are no measurable effects of the polymer on the thickness of the surfactant layer at any concentration. There is an indication that at the surface the surfactant is slightly displaced outward from water on addition of polymer, but accurate structural determination of the mixed layer proved too difficult to be certain of this result.