Revealing complex relaxation behavior of monohydroxy alcohols in a series of octanol isomers.

We investigate the reorientation dynamics of four octanol isomers with very different characteristics regarding the formation of hydrogen-bonded structures by means of photon-correlation spectroscopy (PCS) and broadband dielectric spectroscopy. PCS is largely insensitive to orientational cross-correlations and straightforwardly probes the α-process dynamics, thus allowing us to disentangle the complex dielectric relaxation spectra. The analysis reveals an additional dielectric relaxation contribution on time scales between the structural α-process and the Debye process. In line with nuclear magnetic resonance results from the literature and recent findings from rheology experiments, we attribute this intermediate contribution to the dielectric signature of the O-H bond reorientation. Due to being incorporated into hydrogen-bonded suprastructures, the O-H bond dynamically decouples from the rest of the molecule. The relative relaxation strength of the resulting intermediate contribution depends on the respective position of the hydroxy group within the molecule and seems to vanish at sufficiently high temperatures, i.e., exactly when the overall tendency to form hydrogen bonded structures decreases. Furthermore, the fact that different octanol isomers share the same dipole density allows us to perform an in-depth analysis of how dipolar cross-correlations appear in dielectric loss spectra. We find that dipolar cross-correlations are not solely manifested by the presence of the slow Debye process but also scale the relaxation strength of the self-correlation contribution depending on the Kirkwood factor.

Glassy dynamics in polyalcohols: intermolecular simplicity vs. intramolecular complexity.

Using depolarized light scattering, we have recently shown that structural relaxation in a broad range of supercooled liquids follows, to good approximation, a generic line shape with high-frequency power law ω-1/2. We now continue this study by investigating a systematic series of polyalcohols (PAs), frequently used as model-systems in glass-science, i.a., because the width of their respective dielectric loss spectra varies strongly along the series. Our results reveal that the microscopic origin of the observed relaxation behavior varies significantly between different PAs: while short-chained PAs like glycerol rotate as more or less rigid entities and their light scattering spectra follow the generic shape, long-chained PAs like sorbitol display pronounced intramolecular dynamic contributions on the time scale of structural relaxation, leading to systematic deviations from the generic shape. Based on these findings we discuss an important limitation for observing the generic shape in a supercooled liquid: the dynamics that is probed needs to reflect the intermolecular dynamic heterogeneity, and must not be superimposed by effects of intramolecular dynamic heterogeneity.

On the relationship between gingival morphotypes and different crown shape assessments in young Caucasians.

OBJECTIVES: The objective of this study was to determine the relationship between crown length as well as crown width and gingival morphotypes (primary aim) and their correlation with tooth shape and papilla height (secondary aim). MATERIAL AND METHODS: Thirty-six adult subjects were evaluated in this clinical study according to their gingival morphotype (GM) defined by transparency of a periodontal probe through the buccal gingival margin. Eighteen subjects comprised the thin entity group and 18 the control group thick entity, respectively. Besides crown length (CL) and crown width (CW), two different methods to assess crown shape (CW/CL ratio) were compared and analysis of their relation to papilla height was performed. RESULTS: Nineteen female and 17 male volunteers were enrolled in this study, with a mean age of 24.9 years (±3.4; minimum 18, maximum 35). A statistical significant difference for the crown length could be detected between both groups (p < 0.05) but not for crown width. No significant difference was found for apical or coronal CW/CL ratio besides on tooth 22. CONCLUSION: Within the limitations of this study and within this young Caucasian study population, only crown length seems to have an association with different gingival morphotypes. Furthermore, papilla height and crown shape do not have a clear correlation on tooth level. CLINICAL RELEVANCE: Crown shape seems to be not a strong parameter in assessing the gingival morphotype.

On the relationship between gingival biotypes and gingival thickness in young Caucasians.

OBJECTIVES: To evaluate a possible relationship between gingival biotypes and gingival thickness, papilla height and gingival width. MATERIAL AND METHODS: Thirty-six adult subjects were stratified by their gingival biotype (GB), as defined by transparency of a periodontal probe through the buccal gingival margin, into "thin" (18 subjects) and "thick" (18 subjects) GB. Out of these, extreme cases (6 "very thin", 6 "very thick") were identified. Four different parameters were assessed: gingival thickness (GT), papilla height (PH), probing depth (PD) and gingival width (GW). RESULTS: When comparing "thin" and "thick" GB, midfacial GT (0.40 ± 0.07 vs. 0.72 ± 0.11 mm; P < 0.0001), PH (3.76 ± 0.50 vs. 3.95 ± 0.41 mm, P = 0.02) and GW (3.01 ± 1.26 vs. 4.63 ± 0.86 mm, P = 0.04) were lower in the "thin" GB group. Further stratification into moderately and extremely "thin"/"thick" GB eliminated the differences between the moderate groups. CONCLUSION: Our data support the traditional hypothesis that two different gingival biotypes with concomitant properties distinguishable by gingival transparency exist. In addition, we provide evidence that an alternative classification into "very thick", "moderate" and "very thin" biotypes might be advantageous, because the unique properties were seemingly primarily driven by subjects with extreme values.

Molecular transport and water condensation inside mesopores with wettability step gradients.

The wettabilities of nanoscale porous surfaces play important roles in the context of molecular and fluid transport or oil-water separation. The wettability pattern along a nanopore strongly influences fluid distribution throughout the membrane. Mesoporous silica thin films with gradually adjusted wettabilities were fabricated via cocondensation. With consecutive mesoporous layer depositions, double-layer mesoporous silica films with asymmetric or so-called Janus wettability patterns were generated. The effects of these wetting gradients on mass transport, water imbibition, and water vapor condensation were investigated with ellipsometry, cyclic voltammetry (CV), drop friction force instrument (DoFFIs), fluorescence microscopy and interferometry. By increasing the film thickness of the hydrophobic mesoporous silica top layer deposited on a hydrophilic mesoporous silica layer up to 205 nm, molecular transport through both the layers was prevented. However, water was observed to condense onto the bottom layer, and transport occurred for thinner top layers.

Generic Structural Relaxation in Supercooled Liquids.

One of the unsolved problems of dynamics in supercooled liquids are the differences in spectral shape of the structural relaxation observed among different methods and substances, and a possible generic line shape has long been debated. We show that the light scattering spectra of very different systems, e.g., hydrogen bonding, van der Waals liquids, and ionic systems, almost perfectly superimpose and show a generic line shape of the structural relaxation, following ∝ ω-1/2 at high frequencies. In dielectric spectra the generic behavior is recovered only for systems with low dipole moment, while in strongly dipolar liquids additional cross-correlation contributions mask the generic structural relaxation.

Influence of Molecular Architecture on the Dynamics of H-Bonded Supramolecular Structures in Phenyl-Propanols.

Relaxation behavior of monohydroxy alcohols (monoalcohols) in broadband dielectric spectroscopy (BDS) is usually dominated by the Debye process. This process is regarded as a signature of the dynamics of transient supramolecular structures formed by H-bonding. In phenyl-propanols, the steric hindrance of the phenyl ring is assumed to influence chain formation and thereby to decrease or even suppress the intensity of the Debye process. In the present paper, we study this effect in a systematic series of structural isomers of phenyl-1-propanol in comparison with 1-propanol. It turns out that by combining BDS, photon correlation spectroscopy (PCS), and calorimetry, the dynamics of supramolecular structures can be uncovered. While light scattering spectra show the same spectral shape of the main relaxation for all investigated monoalcohols, the dielectric spectra differ in the Debye contribution. Thus, it becomes possible for the first time to unambiguously disentangle both relaxation modes in the dielectric spectra. It turns out that the Debye relaxation becomes weaker, the closer the position of the phenyl ring is to the hydroxy group, in accordance with the analysis of the Kirkwood/Fröhlich correlation factor. Even in 1-phenyl-1-propanol, which has the phenyl group attached at the closest position to the hydroxy group, we can separate a Debye contribution in the dielectric spectrum. From this, we conclude that structure formation through hydrogen bonds is not generally suppressed by the increased steric hindrance of the phenyl ring, but rather an equilibrium of ring and chain-like structures is shifted toward ring-like shapes on shifting the phenyl ring closer to the hydroxy group. Moreover, the shape of the α-relaxation, as monitored by PCS, is the same as the self-part of the correlation in BDS, remains unaffected by the degree of hydrogen bonding and is the same among the investigated alcohols.