Crystal Growth Detection System

A fast and reliable method for detecting early crystal growth in suspensions is desired.

Background & Impact Statement

Colloidal suspensions are systems subject to thermodynamic and kinetic equilibriums. A key destabilization event of suspensions is known as crystal growth which is a highly variable and difficult factor to control.

Crystal growth is usually observed when a solid can dissolve in the continuous phase (predominantly water for the Seeker’s application) to create a supersaturated phase. In such a suspension there is a driving force for the smaller solid crystalline particles to dissolve, which under certain conditions recrystallise on the surface of remaining solid particles leading to dramatic increases in particle size. This phenomenon is observed most often when variations of temperature occur e.g. cold-warm cycles.

The samples that need to be analyzed are of complex composition and have a high colloidal concentration, ranging from 10 to 50 %w/v and contain complex mixtures of other co-formulants such as emulsifiers, dispersants and gelling agents. The crystal particle size of the samples follows a typical Gaussian distribution, typically 90% less than 5 µm and a median diameter of 2 µm. A complication to the analysis of these systems is that the crystalline particles (under a different colloidal destabilization event) can aggregate which will also lead to an increase in particle size.

So far, the Seeker has tested a number of methods to determine early crystal growth in colloidal suspensions. The tested methods and their limitations are listed below:

• Laser diffraction particle analyzer, type Malvern Mastersizer: This technique measures the relative distribution of volume of particles. Mathematic modeling is used to fit a distribution curve to the measurement. Limitation of this technique is that quantitative measurements are not accurate and it is difficult to detect early crystal growth due to resolution. To be able to detect crystal growth, crystals need to reach a size of at least 30 - 40µm. This implies storage cycling programs that can vary from a couple of weeks to several months to get to that stage. Another drawback of this technique is that aggregates of particles are confounded with large crystals in the measurement.
• Particle sieves, using mesh within the range of 45 to 75 µm: This method consists in diluting the sample in water and then sieving it. If crystal growth occurred, crystals are collected in the mesh. The main limitations of this method is that it is labour intensive and due to the mesh size available, detection of crystal growth requires long storage time.
• Microscopy, using different polarizing techniques: This technique is useful to confirm crystal growth but is neither reliable to monitor its evolution nor give quantitative measurements. Furthermore, due to small sampling size, it is likely that crystal growth can be missed.
• Particle counting methodology, e.g. using the Coulter counting method. This proved to be a suitable method for detecting small variations in particle sizes and therefore useful for detecting crystal growth early on. However a necessary sample preparation step limits the usefulness of this method:. The equipment works with a much diluted dispersion of the sample in an electrolyte solution only. This can lead to solubilisation of the smallest crystalline particles and therefore lead to false results.

In summary the methods tested in the past were hampered by two major drawbacks:

• Ability to detect crystal growth early on (range of 5 to 30 µm).
• Assay time needed to determine the presence of crystal growth.

Through this Challenge, the Seeker would like to identify a method which can detect crystal growth earlier and in shorter time. Solutions can be completely new methods or improvements of the methods listed above. More specifically, your proposed method for the detection of crystal growth shall meet the following Requirements:

Technical

• Can consistently and reproducibly detect crystal growth in the range of 5 to 30 µm in a colloidal dispersion with crystal particles of size <5 µm and ranging from 10 to 50% w/v.
• Ideally can be carried out at room temperature. Measurement techniques requiring elevated temperatures should aim not to exceed 50°C.
• Preferably can distinguish between crystal growth and aggregates.
• Preferably can be implemented as a bench top solution which requires no or only limited sample preparation and produces a data output not requiring further analysis.

Legal

• Both new methods as well as methods lifted from the public domain are of interest.

Your submission will need to include the following to become eligible for the cash award:

• Detailed Description of your proposed method that can meet the Requirements listed above. This may include:
  
  
  
  • Equipment and instrument needed
  • Sample preparation procedures
  • Analytical test procedures with protocols if available
  • Literature references or evidence/examples of effectiveness
• Explanations with rationales as to why the Solver believes that the proposed method will work. These explanations should address each of the Technical Requirements listed above and should be supported with relevant examples and literature citations. If the proposed solution involves an improvement to one of the methods known to the Seeker (see above), Solvers will need to explain in detail how the proposed improvement overcomes the limitations listed for that method.