Observation of gaseous films at solid–liquid interfaces: Removal by ultrasonic action

Micro-structure differences in kaolinite suspensions

“…These chain-aggregates are few lm long and encircling large voids filled with electrolyte 1-10 lm in diameter. These highly porous super-structure build of elongated aggregates and chain associations have been described before in [9,[11][12][13] as a flocculated but dispersed structure. Such gel structured suspensions are typical of those observed in Birdwood kaolinite by SEM [9] are difficult to explain on the basis of DLVO theory because positively charged edges should repel each other.…”

“…The aqueous solution surrounding these kaolinite stacks shows distinctive gaps between the water and solid surface at several places as well as apparent voids within aggregates. This type of gaseous bubbles and film presence was detailed described in [12] where cryo-SEM investigations revealed that water not wetting mineral surface leaving gaseous film on the solid/liquid interface. The gaps adjacent to the mineral surface are 80-100 nm thick and appear to continuously cover substantial parts of the aggregate surfaces.…”

“…As an explanation of the predominance of such contacts it is proposed in [13] that hydrophobic like attraction between aerated edges may occur and platelets may rolling on top of each other with help of air micro-bubbles well-described in [12]. Such mostly EE linked particles build long strings seen in two dimensional SEM images as sections of planar structure that connect to each other to build a spacious cell structure as shown in Fig.…”

“…There is a clear association of CH _ fragment images with both Al+ and Si+ images possibly suggesting partially hydrophobic species but there is no evidence of any effect of these species on the electrokinetic behaviour of the kaolinite and carbonaceous contamination of surfaces is well known to be ubiquitous. If present, however, even in small concentrations, surfactants would also help to explain the stability of the micro-bubbles and even gaseous film in the mineral interfaces detailed described recently in [12]. Georgia Kaolinite KGa-1 has not been investigated in ToFSIMS technique.…”

“…This gaseous gap may be because of hydrophobic interaction between siloxane layer of kaolinite crystals and water. Such a gaseous blanketing at the mineral interface can be eliminated by ultrasonic treatment [12]. Hydrophobic interaction between clay particles surrounded in such blankets was nominated as the major factor in aggregation and structure building in [14].…”